After Hours Data Systems: EPA 608 Practice

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 2018. 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 Unpublished every other app to focus.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, LLC formed

Rebuilt the Android version end to end and shipped the first iOS version on Thunkable. Formed the LLC. Revenue grew sharply from this point. The dual-platform rebuild is what unlocked the inflection.

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.

Honest framing

I have never written native iOS in Swift or native Android in Java/Kotlin. The story is visual / low-code (App Inventor, Thunkable) and now cross-platform Flutter / Dart. iOS shipped in 2018, not 2014.