I've started work on a project I call SDLRPG. It's meant to be a competitor (I don't think clone is the right word for it) of RPG Maker XP, including such features as same resource formats and Ruby scripting, but cross-platform, with support for plugins (insert combat system here) and the like.
So far, the game engine itself isn't anything to look at (loads FMOD, SDL, and Ruby) but the game editor is another matter. Rob Loach might be happy to hear that the editor makes use of SdlDotNet for the graphics.
Right now, the whole thing is in two projects, the Editor and the Engine. I'm planning to separate some of the classes in the Editor that could be of use in the engine (or other projects looking to take advantage of SDLRPG) and rewrite them in C++. (I'd create a .Net assembly to call on the resulting library, much as SdlDotNet sits upon SDL).
I started writing the engine in C++ and it'll remain that way since I'm used to C++ and SDL, and it's far more portable than C# is. (Mono withstanding, but not everyone has that.) The editor may not be portable as it is, but being written in C# and designed with Visual Studio allows me to do some nice rapid application design (the entire editor, as it is, was only started on Monday night), and while it will be rewritten in the future, possibly the very near future, I'm planning to keep it .Netted.
Beyond SdlDotNet, the editor uses the Scintilla text edit control via the creatively named ScintillaNET wrapper, to provide the script editor. Also, the menu bar and toolbar are done using Lutz Roeder's CommandBar assembly. (If you do lots of .Net programming, and haven't heard of this guy, make your way there now. Useful goodies.)
I won't be doing much coding this weekend, but chances are I'll be redoing the editor much as I described (and this time, take advantage of user controls; damn layout is convoluted as all hell, and inefficient to boot). Then I'll probably do some work on the engine so it can play with whatever data I can get the editor to create.