GDevelop, a FOSS (Free and open-source software) 2D game engine seems to be really coming along nicely for the current overhaul.
Tools like GDevelop are incredible for quick prototyping, introducing a younger generation to developing and professional games too. What I love about GDevelop, is that it uses a visual programming events system. It could be compared with Clickteam's Fusion or Scirra's Construct.
It's been quite some time since checking up on it and it seems they're still polishing up the big 5.0 version with a 79th beta being released only recently. Lots of new features added this year too like mouse scroll support, a much improved editor to add and edit conditions and actions, a more responsive UI, a new gamepads extension (which I tested working perfectly with my Logitech F310), the ability to search for and add extensions to your projects, they added copy/cut/paste for events functions and custom behaviours, a brand new Physics engine, a new action to take Screenshots of the game and a ton more.
Over time they've also added quite a few more game/demo examples like an 8-bit space shooter which shows off the custom behaviours system and a local multiplayer platformer with gamepad support.
Honestly, I'm really impressed with what they've done here to the point that I might even start messing with it to make something.
Want to know what's been made with it? Hyperspace Dogfights is a good example and it's a really fun game too that's worth a look.