Vocastar UltraDeluxe
My current side project. For the lack of an easy to setup, resource friendly and cross platform Singstar clone, I started to build my own. It's written in Kotlin Native with a few C interop libraries for handling A/V. Very much WIP and not Github ready ;) SQS-Connect
When I integrated Amazon SQS for my former employer I wasn't satisfied with the available JCA adapter options. I see the benefit of contributing to existing open source projects, but as I also wanted to learn what a JCA adapter exactly does - and how. So I built my own, and while there is still something to do (is a project ever really done though?), I'm pretty happy with what I got.
Project page Filegur
Every now and then, you need to share large files. But email attachments only get you so far, and free hosters often are quite ad-riddled these days. So what'd be more natural than to just roll your own?
Project page M3C
I started programming by developing Minecraft server plugins. So when I wanted to learn how server - client communication works on a network packet level, it was only logical for me to dive into the game's protocol. After it was done, I had a working (plugin extensible) console client!
Project page