Tenant
TR

One React codebase. 30+ exchanges and brokerages. Each with its own brand.

I'm Berkay Gülşen, a Senior Frontend Engineer and Team Lead in Istanbul. 8+ years with React and React Native, mostly in fintech and trading.

Open to Frontend Team Lead and Senior Frontend roles · Remote or Istanbul

At Optimus, every firm got its own theme from one codebase. This site works the same way. Pick a tenant:

Selected work

  • Multi-tenant React SDK

    Optimus Yazılım · –

    Role
    Senior Software Engineer
    What I built
    Co-built a multi-tenant React + Redux SDK covering both UI and infrastructure. One codebase; each firm ran it with its own branding, themes and business rules. I also built C# (.NET Core) and Go services that process concurrent financial transactions and market data.
    Outcome
    Used in production by 30+ exchanges and brokerages.
    • React
    • Redux
    • Ant Design
    • C#
    • .NET Core
    • Go

  • Crypto exchange, web and mobile

    Crybo · –

    Role
    Frontend Team Lead, leading a frontend team of 2 developers
    What I built
    The exchange's web and mobile apps with React, Next.js, React Native and Redux: real-time trading screens, KYC onboarding and the complete user flow. I worked daily with the backend developers on API design and integration.
    Outcome
    The product was finished and passed internal testing; trades executed end to end. The company wound down before public launch.
    • React
    • Next.js
    • React Native
    • Redux

  • Health-tech platform, built alone

    Fluxivo · –

    Role
    Technical Lead and the company's only engineer (part-time Feb–Jul 2024, full-time from Aug 2024)
    What I built
    The whole product from scratch: a Go and Node.js backend (PostgreSQL, Prisma) handling real-time telemetry from IoT devices such as spirometers and smartwatches; a React web app and a React Native mobile app synced through Firebase; infrastructure on AWS EC2; and an AI health assistant running Python models on AWS SageMaker.
    Outcome
    Shows I can own an entire system alone, from device data to the mobile UI.
    • Go
    • Node.js
    • PostgreSQL
    • Prisma
    • React
    • React Native
    • Firebase
    • AWS

My own products

  • Rider OS screenshot

    Rider OS

    Launching October 2026

    An app for motorcycle riders: group rides, SOS, garage and maintenance tracking.

    Built solo

    • React Native (Expo)
    • Go
  • Hocam! screenshot

    Hocam!

    Launching October 2026

    A swipe-based teacher simulator game: get a primary school teacher through a 36-week school year, balancing students, parents, administration and your own energy.

    Built solo

    • Expo
    • TypeScript
  • Lilla screenshot

    Lilla

    Launching October 2026

    An at-home beauty services platform: customer and specialist apps, Go API, admin panel, and safety flows for specialists visiting homes (door PIN, panic button, expiring location links).

    Building with a partner

    • React Native (Expo)
    • Go
    • Next.js

How I work

Experienced engineers don't vibe-code. Building software without AI today is like farming without a tractor. It does the heavy lifting, and my time goes into architecture and optimization.

I can own a frontend from architecture to release, including component systems, state management, real-time data and performance. I've also written production backends in Go, Node.js and C#, so API discussions with backend engineers stay short.

Experience

  1. – Present

    Independent Product Engineer

    Self-employed

    Rider OS, Hocam!, Lilla

  2. –

    Frontend Team Lead

    Crybo

    Crypto exchange, web + mobile

  3. –

    Technical Lead

    Fluxivo

    Health-tech, only engineer

  4. –

    Senior Software Engineer

    Optimus Yazılım

    Multi-tenant React SDK, 30+ firms

  5. –

    Software Engineer

    Multytude (London, remote)

    AI survey platform, React, React Native, Go

  6. –

    Software Engineer

    Optimus Yazılım

    Portfolio management apps, React, C#

  7. –

    Software Engineer

    Finartz

    E-wallet, C#/.NET, Vue.js

  8. –

    React Developer

    Piksel Mutfak

    neredekal.com, Next.js SSR

  9. –

    Frontend Developer

    ASNAK Logistics Technologies

    Logistics and auction platform, real-time

  10. –

    Frontend Web Developer

    Freelance

Speaking

Build with AI: Web Development Bootcamp

TurkStudentCo, online · 22 May 2026

Environment setup, coding with prompt techniques, and web hosting.

Stack

  • Frontend

    • React
    • React Native
    • Next.js
    • TypeScript
    • Redux
    • Expo
    • Apollo GraphQL

  • Backend

    • Go
    • Node.js
    • C# / .NET Core
    • PostgreSQL
    • Prisma
    • MS SQL Server

  • Cloud

    • AWS (EC2, SageMaker)
    • Firebase
    • Docker

Contact

Hiring a Frontend Team Lead or Senior Frontend Engineer, remote or in Istanbul? Email me, or message me on LinkedIn.