Eldritch Enterprises is a gaming company that partners Frank Mentzer, Jim Ward, Tim Kask, and Christopher Clark. They formed last year and been relatively quiet. Now they have finished their first four product and have released them as PDFs on RPGNow/DrivethruRPG. They are:
Lich Dungeon - Level One
Snakeriders of the Aradondo
Forest of Deceit
I haven't had the chance to review them yet however there is one cautionary note. If you look at the previews (for example Lich Dungeon), you will see that they chosen not to use the OGL and use a very odd stat block format. That wouldn't be so bad but it also takes up as much space as a d20 style stat block. So you should read over the previews first to see if this a deal breaker for you.
Frank Mentzer said Eldritch is talking to the publishers of the various retro-clones so in the future the situation may change.
Update: Frank has posted a link explaining how the stat block works.
GURPS Gamma World, 20th Homeland - Session 5
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