APIs & integrations
For most non-trivial products, the API layer is where user-facing behavior becomes durable business logic. I design and integrate APIs around clear contracts, authentication, validation, idempotency, failure states, callbacks, observability, and the relational state behind them.
What this looks like in practice
Core technologies
Project evidence
Each project below links to a deeper case study covering product scope, engineering ownership, supporting systems, and production evidence.
Enterprise · Case study
Rent collection and reconciliation software for landlords and property managers. RentPayor connects iOS and Android apps with a web management dashboard for landlords and property managers. It handles properties, leases, rent invoicing, M-Pesa collections, partial payments, automatic reconciliation, receipts, credits and reporting.
Read case studyEnterprise · Case study
Hospital management information system connecting patient registration, OPD, emergency, inpatient care, orders, referrals, theatre, billing, ambulance, mortuary, duty coverage, patient movement, documents, and facility operations. It includes facility-bound Tuma M-Pesa patient billing and reconciliation, alongside SaaS subscription billing infrastructure.
Read case studyEnterprise · Case study
Cargo and logistics operations platform spanning mobile field workflows and back-office administration. Macsim handles loads, reservations, driver assignments, trip tracking, documents, notifications, fleet operations and finance, with a guarded M-Pesa/Daraja flow for funding a collection-account ledger and paying drivers in full or partial load installments.
Read case studySaaS · Case study
Voice-first journaling app that preserves the original recording, transcribes spoken entries, and uses AI to generate useful titles, summaries, and categories. Entries can be searched and revisited by date, linked to goals, supported by reminders and prompts, and protected with account, deletion, and optional biometric controls.
Read case studySaaS · Case study
Mobile wardrobe-management and outfit-recommendation product. Users create wardrobes, upload clothing photos for AI-assisted category, tag, and description analysis, and generate one-time, daily, or weekly outfit suggestions that can use precise local weather; recommendation history is stored locally in SQLite and designed to sync with the cloud.
Read case studyLet's build something that lasts
Talk directly with the engineer responsible for your project. Joeltech Geek Systems works with businesses and founders in Kenya and across the world.