Unity itself offers a free version of its 3D game engine at all times. However, the tools to release Unity games for mobile phones is currently available for free as well (only until April 8th), normally these cost $800.
Available here: https://store.unity3d.com/index.html
Select the FREE version of Unity, then the two mobile versions below it, then hit Add to Cart and Checkout. You won't even have to give it a credit card, just basic account information and your address (there is also an optional survey about what you plan to develop with it).
Even if you don't have any plans or interest in using these at the moment, it is probably worth taking 30 seconds to create an account and acquire the keys for this $800 software while it is free.
In a related note, Unity says "When you shine, we shine". An impressive mindset, one that the BYOND staff and developers should strive to adopt, and actually work towards. I saw Tom addressing somebody in the forums a few days ago with something that essentially said "Our engine sucks, use something else". Not exactly a shining beacon to guide the community...
Mar 15 2012, 9:28 pm (Edited on Mar 15 2012, 11:26 pm)