I'm using...
GitHub for versioning
Trello for project management
Coding in Notepad++
Libraries Kiwi.js and possibly some other stuff I've collected.

I'll be testing on a Windows phone (not a fan) and my Kindle Fire. Touch support could be the biggest issue, but it looks like Kiwi.js has that covered.

I will use Game Maker:Studio (1.4) because it has all of the features that I want for example:
-Cross-platform building (Focusing on windows nor HTML5 but try to be put on android if the game mechanics will allow it.. :D )
-full featured 2D game framework
- and..I just bought it a couple weeks ago on Humble-bundle so for me, it will be fully legal develop with this great engine :D

That's cool. I just bought Game Maker too, but it will have to wait until after the jam.

I'm using gamemaker as well for this one, and it's my first time fiddling with it, so I'm a little nervous. Gonna start with playable proof of concept then try to work the harder to code ideas into it

Just going to say that prototyping saved me on this. It helped me cut feature in the right places and get things submitted before the deadline. Would have loved to do more, but what game jammer didn't feel that way?