The last 15 month I spent my spare time working on a HTML5 based online shooter. I call it kugeln.io.
It's not released yet, but I'm getting closer every day.
As you may noticed, I got inspired by Teeworlds. The controls are almost the same. A big difference is, that the environment is destructable and has some gimmicks like machine guns.
I chosed HTML5/web as a platform, because everyone knows how to use a web browser. For many people it sounds very strange, but not everyone knows how to use Steam or extract a ZIP file. And even if they would know how to use it, they don't see a reason to download it.
In case you also spend way too much time on the internet, you have probably noticed that it's a countryball (also called polandball) themed game.
Why? Because I love them. ;-)