PlayCanvas goes open source (opens in new tab)

Broadly speaking phaser is 2D, PlayCanvas is 3D. (Though you can always do 2D stuff in 3D)

Full disclosure: I know the guys who made this. I won't compare it against the competitors since I haven't used alternatives but my 2 cents:

1) This has been years in the making--these guys have spent the last couple of years focused on making the best tool possible.. days nights and weekends! 2) They're super passionate about games/gamers.. they've organized gamejams and html5 meetups and are really in touch with the community. They're in this 100% and very open to feedback--so expect loads of improvements in the next couple of months!

I haven't used it, but I remember looking at the minified code a while back when it was first released. It looks very well done, by someone who has excellent game-engine design experience.

THREE.js is very low-level framework, while PlayCanvas additionally to low-level engine access has game framework, which will allow you to create game logic and scripting in much better way.

Just because you can view the source code does not mean that it is open source.