Has anybody tried using this?
I've been wanting to write my games to work on multiple platforms but the only solutions I've seen up to now are complete authoring packages such as Unity or UDK. I wanted something a little lower level without having to roll my own and create all the boilerplate code for all the different platforms. This seems to fit the bill and is completly open source.

I am also looking for the current state of low-level multiple platform support.

Gameplay looks like an interesting one, did not try it yet but seems solid.

You may want to look Proton SDK as well, although I will risk to say that Gameplay is probably more solid (I mean, less buggy).

I checked Proton a month ago, and although I found it quite interesting, I felt it a bit messed up yet -- which I understand, as that one is quite new yet and from individuals, not a company.

If you try one or both, please tell us what were your impressions.