Rostislav Kozak

@Berliner187 · kozak187er · indie developer

I run Letychka, a SaaS that turns lecture files into online tests. I also write a dictation app for macOS in Swift. At work I build BI and ETL for companies: Airflow pipelines, Visiology dashboards, semantic layers.

main product since 2024

● running

LetychkaЛетучка

A teacher uploads a PDF or DOCX, or pastes text, and gets a ready online test. Students open it by link or QR code, with no registration.

Built for teachers, tutors, university departments and company training teams. Answers are checked automatically, and the teacher sees which topics students got wrong most often.

4500+users
RUinterface
input
PDF, DOC/DOCX, TXT up to 25 MB, or pasted text up to 100,000 characters
tests
Three difficulty levels, single or multiple correct answers, shuffled options, editing of any question after generation
students
Link or QR code, no account needed
results
Automatic scoring, per-question statistics, Excel export, printable A4 sheets in two variants with an answer key

python / django / postgresql / redis / celery / llm

other projects 2023–2026

  1. ● in development

    GolosokГолосок

    Offline dictation for macOS. Press ⌥ Space, speak, and the text appears at the cursor in any app. Recognition runs locally on GigaAM v3 or Whisper, using the GPU and Neural Engine of Apple Silicon, so audio stays on the Mac.

    • v1.13.9
    • MIT
    • macOS 13+
    • Apple Silicon
    • free

    swift / metal / core ml / gigaam-v3 / whisper

  2. running

    Taxi Watcher

    A Telegram bot that watches ride-hailing prices on a chosen route and writes when the fare drops.

    python / asyncio / telegram bot api

archive · 2 early repos

Personal projects that were never released and are no longer maintained. The code is on GitHub as is.

  1. unmaintained

    Finanzfluss

    Command-line budget tracker: income, expenses and account balances.

    python / cli

  2. unmaintained

    Elba

    Offline password and notes manager with local encryption. GPL-3.0.

    python / cryptography

stack

products
Python, Django, FastAPI, PostgreSQL, Redis, Celery, Docker. Swift, Metal, Core ML on macOS
data & bi
Apache Airflow, ETL, Pandas, SQL, Visiology, semantic layer design

elsewhere