Ah yes the owner would be me, and I really have to get around to releasing a new version of REXPaint xD. Lots of potential feature ideas, and it's cool to have to many people using this little tool I originally made for my own projects!
I've also already got a little backlog of great art by users from recent weeks that I still need to add to the gallery...
Also see the editor used for creating the art in that gallery: http://www.gridsagegames.com/rexpaint/
Note that I'm not the owner of the subreddit I'm just a user.