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Salah Abdelkhalek
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Available: full-time, remote & freelance

Salah Abdelkhalek

Founder & Senior Full-Stack Engineer

I ship complete products, from Rust backends and AI agents to the interface people actually touch.

Sousse, Tunisia

How I build: every layer

  1. 01

    Interface

    Everything people see and touch. I build fast, accessible web apps, React Native mobile apps and premium websites with motion and 3D, so the experience feels effortless on any screen.

    React · Next.js · TypeScript · React Native · Expo · Three.js

    AdvantageFast, accessible, memorable.

  2. 02

    API

    The front door of every product. Each request is authenticated, validated and routed through clear REST or GraphQL contracts that other teams can build on, documented with OpenAPI.

    REST · GraphQL · Apollo · JWT · Zod · Swagger

    AdvantageSecure, predictable contracts.

  3. 03

    Bus

    Services talk through events instead of waiting on each other. Message queues, webhooks and real-time channels keep the platform responsive under load and keep payments in sync.

    RabbitMQ · WebSockets · Webhooks

    AdvantageResponsive under load.

  4. 04

    Services

    Where the business logic lives: multi-tenant platforms, billing and subscriptions, notifications and autonomous AI agents that wait for a human approval. Written in NestJS or Rust, depending on the job.

    NestJS · Node.js · Rust (Axum) · Microservices · LLMs

    AdvantageLogic that scales cleanly.

  5. 05

    Data

    Where everything is stored and searched: relational and document databases, caching, object storage and vector search for AI, designed for correctness first, then speed.

    PostgreSQL · MongoDB · Redis · MinIO · Qdrant · Meilisearch

    AdvantageCorrect first, then fast.

Full stack

End to end.

One request, five layers. I design, build and ship all of them.

01About

Complete products, shipped end to end.

I'm a senior full-stack engineer with 6+ years of shipping production software end to end, from the database schema to the last pixel.

Most of my work sits where reliability matters: financial platforms, multi-tenant SaaS, distributed backends and AI systems, from hybrid RAG search to autonomous agents with a human in the loop. I work daily with Node.js/NestJS, TypeScript, PostgreSQL, Rust and AWS, and I take products all the way to the user: web apps, React Native/Expo mobile apps and premium websites.

Today I run my own studio, RE_UNDERSCORE. I've led a team of 5+ engineers, mentored juniors, and set up the code reviews, tests and monitoring that keep production calm. I work in English, French and Arabic.

Sousse, TunisiaArabic · French · English

  1. 01

    Backend & fintech

    Microservices, multi-tenant platforms, payments and financial workflows.

  2. 02

    AI systems

    Hybrid RAG search and autonomous agents with a human in the loop.

  3. 03

    Web & mobile products

    Next.js and React apps, React Native/Expo mobile apps.

  4. 04

    Premium websites

    Fast, accessible websites with motion and 3D.

02Selected work

Systems where reliability matters.

Two case studies: a fintech platform I built and own, and AI search at scale.

OCR → data → ledgers

Fintech · Bank draft management

Combium

Bank drafts are still a paper instrument. Combium turns them into data: drafts are captured by photo (OCR), printed precisely on the official forms, tracked per company and summarized every morning by WhatsApp or SMS.

  • Multi-tenancy
  • OCR
  • Document printing
  • WhatsApp & SMS
  • Financial reporting

Own product

Hybrid retrieval

AI · Hybrid RAG search

Truth Chatbot

The backend of an AI chatbot that answers from the Quran and Hadith. Built in Rust, it combines semantic vector search (Qdrant) with full-text search (Meilisearch) to ground every answer in 7M+ records of hadith, tafsir and related texts.

  • Rust
  • Qdrant
  • Meilisearch
  • Hybrid retrieval
  • RAG

Built at Celestial Wave Digital

03AI Agents

Automation you can trust.

Two autonomous agents that take on the repetitive work of growing a business, with a human approving every result in one click.

Approval gate

01 / 02

Social Media Agent

Plans, writes, designs and publishes Instagram and Facebook content. LinkedIn is next.

How it works

  1. 1Pick a topic: seasonal, never repeated.
  2. 2Write the on-image text, caption and reel script, each checked automatically.
  3. 3Design on-brand visuals and vertical reels, generated in code.
  4. 4Send for approval, then publish on schedule.

Impact

A steady, consistent presence, for a few minutes a day.

Approval gate

02 / 02

Prospecting Agent

Finds businesses that would benefit from a website, qualifies them, and writes each one a personal email.

How it works

  1. 1Search company data, area by area.
  2. 2Qualify and score each business; skip those already well served.
  3. 3Audit their online presence to choose the right angle.
  4. 4Write a personal email, send it after approval, follow up once.

Impact

A continuous flow of qualified leads, with no manual research.

Public contact details only · opt-out in every email · one follow-up maximum.

I build agents like these for other businesses.

Discuss an AI agent

04Websites & redesigns

Websites & redesigns

Websites I designed and built, including concept sites that show the quality a client gets, in French, Arabic and English.

  • Responsive and adaptive

    Designed mobile-first: the layout adapts from phones to large screens.

  • 3D and motion, even on mobile

    Heavy on 3D and animation, yet smooth and usable on a phone.

  • Three languages

    French, English and Arabic, with a right-to-left layout for Arabic.

05Other projects

Platforms, SaaS and custom engines.

  • SaaS · Fitness coaching

    PowerUp

    My own SaaS for fitness coaches: a web dashboard for coaches and a mobile app for their clients. From a prompt, the client's data and the health stats they enter, its AI generates personalized workouts, exercises and meal plans.

    Own product

    • Rust (Axum)
    • MongoDB
    • MinIO
    • Lemon Squeezy
    • Expo
    • LLMs
  • Multi-tenant platform

    Car Rental ERP

    A multi-tenant management portal for car rental agencies, where each agency's data stays isolated on one shared engine.

    • NestJS
    • PostgreSQL
    • React
    • Multi-tenancy
  • Booking · Real time

    Airport booking engines

    Booking engines with real-time flight tracking and route pricing calculated from Google Maps routes.

    • Real-time
    • Google Maps API
    • Pricing engine
  • E-commerce · Supply chain

    VIF

    The backend of VIF, a beauty and cosmetics e-commerce and supply-chain platform, on a carefully designed PostgreSQL schema.

    Built at Celestial Wave Digital

    • NestJS
    • TypeScript
    • PostgreSQL
    • TypeORM
  • Sports management

    Universel Sport

    The backend of a sports management platform.

    Built at Celestial Wave Digital

    • NestJS
    • TypeScript
    • MongoDB
    • Mongoose

06Experience

Six years of shipping to production.

Pick a period on the timeline to see the role, the results and the tools.

Oct 2025 – Present · Sousse, Tunisia

RE_UNDERSCORE (opens in a new tab)

I founded RE_UNDERSCORE to design and deliver complete products end to end: architecture, backend, front-end, mobile, deployment and premium websites.

  • Rust (Axum)
  • NestJS
  • PostgreSQL
  • MongoDB
  • MinIO
  • React
  • Expo
  • Lemon Squeezy
  • Google Maps API
  • OCR

Founder & Senior Full-Stack Engineer

Oct 2025 – Present

  1. Engineered Combium, a bank draft (lettre de change / traite) management platform: high-precision print workflows, OCR photo parsing, automated WhatsApp/SMS daily digests and multi-tenant financial reporting.

  2. Architected and deployed PowerUp, an AI fitness SaaS: Rust (Axum) API, MongoDB, MinIO storage, Lemon Squeezy billing (webhooks, subscriptions, automated lifecycle) and an Expo mobile app.

  3. Built a multi-tenant Car Rental ERP management portal with NestJS, PostgreSQL and React.

  4. Developed airport booking engines with real-time flight tracking and route pricing from Google Maps routes.

  5. Designed and built two autonomous AI agents (social media and prospecting) on a self-hosted open-source model, with a human approval before anything goes out.

  6. Delivered premium websites and redesigns.

07Leadership

Teams that ship, code that holds.

Seniority shows in what the people around you can do. Here is what changed when I led.

  1. 5+developers led

    Lead the team

    Promoted from developer to technical lead at DunDill, I guided a team of five-plus engineers through external client projects, from first commit to delivery.

  2. 25%shorter delivery timelines

    Ship on schedule

    Projects landed on the agreed dates, and the time from start to delivery came down by a quarter.

  3. 40%fewer production bugs

    Raise the quality bar

    Rigorous code reviews and automated tests on every change, plus DataDog monitoring, so fewer bugs reached users and incidents were resolved faster.

08Engineering principles

How I build, whatever the project.

The same habits run through the fintech platforms, the SaaS products, the AI systems and the websites.

  1. 01

    One owner, end to end

    From the database schema to the last pixel, one person accountable, so nothing gets lost between layers.

  2. 02

    Reviewed and tested

    Code reviews and automated tests before anything reaches production. As a team lead, that cut production bugs by 40%.

  3. 03

    Watched in production

    Monitoring on live services, so problems are seen early and incidents are resolved fast.

  4. 04

    Built to stay fast

    Microservices, asynchronous queues and tuned queries keep systems responsive as usage grows.

  5. 05

    Data kept apart

    Multi-tenant by design: each client's data stays separate. AI can run on a self-hosted model when privacy matters.

  6. 06

    AI with a human in the loop

    The model drafts and searches; ordinary code filters and checks; a person approves what goes out.

09Skills & stack

The right tools, for every layer.

01

Backend & APIs

Services and contracts
  • Node.js
  • NestJS
  • Express.js
  • Rust (Axum)
  • REST
  • GraphQL
  • Apollo Server
  • Microservices
  • RabbitMQ
  • WebSockets
  • JWT
  • Passport
  • Zod
  • Swagger / OpenAPI

10Education & certifications

Education, certifications and languages.

Education

  • National Engineer's Degree in Electrical and Automatic Engineering

    École Polytechnique de Sousse · 2015–2020

    Embedded systems integration, automated process control, software engineering

Certifications

  • Google Cloud Fundamentals: Core Infrastructure

    Coursera

  • Graph Developer — Associate & Professional

    Apollo GraphQL

  • Intel Edge AI Certification

    Intel Corporation

Languages

  • Arabic

    Native

  • French

    Professional proficiency

  • English

    Professional proficiency

11Contact

Let's build something.

Tell me about the role, the product or the website. I reply within two working days.