Scid vs PC is probably my favorite interface. I now find myself using that one for all of my GUI needs.
It's a fork of Scid. The Scid program itself is no longer being maintained, and hasn't been for quite awhile. You can read a little bit about Scid's history here:
http://scidvspc.sourceforge.net/
(Click on Miscellaneous and then scroll down.)
The latest version of Scid vs PC, version 4.8, was just released last week, which introduces a bunch of new features.
Last night I had a question or two for the author, and he responded right away. We've corresponded in the past, too. This of course is one of the advantages of using freeware and shareware... the actual author is often very accessible. (Try finding the author of a commercial GUI, let alone talking to him.)
With Scid vs PC you can use your own bitmaps for the piece squares, the program supports both UCI and xboard engines, you can choose between different chess piece fonts, board sizes and board colors, you can have engine vs engine tournaments from any start position, you can have different engines all analyzing the same position, you can connect and play on FICS, the Free Internet Chess Server, you can use an engine to analyze and annotate your games, it's database capabilities can handle LARGE files, (loaded a database with 8 million games in it the other day, with no problems. Note that I did have to first convert it with a little utility that comes with the program, to transfer my pgn files to a binary format for the program.) you can paste in FEN positions that you find online... etc., etc., etc.
Anyway, the list goes on and on and on and on... I'm STILL learning about MANY of the features. I can't say enough good things about it.
When I get home form work, maybe I'll jump back here and post a few screenshots.
Has anyone used SCID vs PC? I guess this is the newest version of SCID. How do you like it and problems, etc?
thanks