I've begun the playtest of Tribute Aleph, the first part of Tribute Source. Tribute Source is an Effects-based RPG design toolkit and series of related games.
If you're interested, you can read more about it, and sign up for the playtest on this page.
If you've never been part of a playtest, be warned. The rules are not in their final form, and as of now, only the toolkit aspects of Tribute Aleph are ready for use. Like other toolkit engines like Fudge, you'll need to make some decisions to make it work.
Thanks for reading.