Founder · After Hours Data Systems · Since 2014
EPA 608 Practice App
Skills exercised
Self-published HVAC certification study app for technicians preparing for EPA Section 608. Available on Apple App Store and Google Play Store. Built and run by me as a single-owner LLC formed in 2021. Operates as passive income today.
The product
- Audience: HVAC technicians studying for EPA Section 608 certification (Core, Type I, Type II, Type III).
- Platforms: Apple App Store and Google Play Store.
- Current stack: Flutter / Dart, cross-platform builds for iOS and Android from one codebase.
- Public signal: 4.0 stars, 110+ ratings on the App Store.
- Status today: stable on both platforms, generating recurring sales, content refreshes only when EPA material changes.
Three platform generations
2014–2018: App Inventor era
Built the first Android version in App Inventor (MIT's visual block-based programming environment), along with around 20 other experimental apps. Only 608 Practice was earning money (~$500–$800/month). Unpublished every other app to focus.
2018: Thunkable rebuild, first iOS release
Rebuilt the Android version end to end and shipped the first iOS version on Thunkable. Revenue grew sharply from this point. The dual-platform rebuild is what unlocked the inflection. The business was later formalized as an LLC in 2021.
Current: Flutter
Migrated the codebase to Flutter for modern cross-platform development. Updates are driven by platform-compatibility changes and EPA exam-content updates. Average annual workload is a few days during the winter off-season.
Companion content tooling
Python tooling for source-question scraping, deduplication, and ingestion into the app's question bank. Keeps the content pipeline maintainable when EPA exam material changes.
Business operations
Everything handled directly as sole owner: LLC formation, accounting, Apple Developer Program, Google Play Console, App Store Connect submission and reviews, tax filings, payment processing, customer support workflow, revenue tracking.