Another option you may wish to consider is PICO-8?
It’s a fantasy 8-bit console (essentially a gamedev engine) for making, sharing and playing tiny games and other computer programs.
The PICO-8 console/engine is designed to have limitations (code/screen/colours/etc.) - so don’t expect to create the next AAA title on it, but the limitations actually help you to stay focused on creating gameplay - and also makes it quite good for prototyping.
It’s not free, but it’s only a one-off cost of $14.99 - and that allows you to export to Web, as well as Win, Mac and Linux binaries. It’s a self-contained system, with integrated: Sprite, Map, SFX and Music editor all built-in.
People have successfully got the Raspberry Pi build to work on the GameShell, see here for a guide.
Anyway, something else to potentially consider! 