Ed Schröder, the author of chess programs such as Mephisto MM IV and MM V, Rebel, and Pro Deo, has decided to make his older Rebel PC chess programs Winboard and UCI (via WB2UCI) compatible and provide them as donationware. As stated at Wikipedia and Ed's site, donationware is a licensing model that supplies fully operational unrestricted software to the user and requests an optional donation be paid to the programmer or a third-party beneficiary (usually a non-profit). Ed's request for donations is for raising money to create a "World Championship" competition among the top-rated chess engines. So feel free to download the versions of Rebel that Ed converts and makes available. If you can, please donate 1 Euro (via PayPal) for each engine you download.
At the moment, Ed has converted Mephisto Gideon Professional (the first Rebel software for PC). It is the engine that won the 1991 World MicroComputer World Championship, and won the 1992 World Championship (via a RISC PC card versus mainframe and specialized chess computers). Here are a few games where I matched Mephisto Gideon Professional against older engines (Crafty 15.00, Arasan 6.3) and newer programs (RumbleMinze 126.96.36.199, ProChess 101CP):
The time control was 40 moves in 7 minutes on a Pentium IV (so these are not high quality games). I used a common book for all engines. If in the future I provide more games for Gideon or other engines, I will let them use their own books.
Here is a game played between Delphil 2.9f and Mephisto Gideon Professional, sent to me by Gabriel LEPERLIER: