I remember someone posted a while back about CraftStudio here ( http://craftstud.io/ ) and I felt like its successor "Superpowers" should also get a mention now that it's gone Free & Open Source as of yesterday and looks like a lot of work has gone into making it into a sweet indie game development tool already
It's HTML5 and WebGL based as well, defaulting to a built-in ThreeJS-based TypeScript engine ready to go out of the box, but what's really cool about it is that it doesn't just allow people to work together, but they actually develop the games right in their browsers too! People run the server, then point their browsers to it and get to work
Also cool is that it's very flexible with what it can be used to make, since its ThreeJS engine can be swapped out for others like say LOVE 2D which is LUA based, or even Node.JS itself based on what I've been reading on their site.
Like how Godot Engine seems to be coming along nicely too it's always great to see more options available for indie developers, especially with the collaborative/real-time editing which feels like the right direction for people doing game jams or working remotely together Hopefully someday Superpowers gets a visual scripting system similar to the block system of Craft Studio or Construct
Press kit: https://bitbucket.org/superpowers/press-kit/src