Does anybody know of a decent (meaning preferably free
;)) alternative to Impact? Any suggestions are very much appreciated!
There are a few here's a list of some:
Crafty (open source)
MelonJS (open source)
LimeJS (open source)
These are all free, and seem fairly finished. I don't know much about the Lime and Melon, but Crafty has a decent community where you can get help in their forums. Which you choose depends on what you need.
Playin looks pretty good. It's free and open-source game library from Google. It was used for conversion of Angry Birds to Chrome browser. Games written in playin should run both in Chrome and Android phones.