I've always liked this little program. An aquarium for your screen, with fish swimming around on your desktop. It traces its history to the xfish program, written around 1987 by John Bradley. Jonathan Greenblatt ported it to X11 in 1988 and it made its way into the contributed program collection by about X11R6. Eric Bina worked on the color maps and root window support and added a lot more fish around 1992. TJ Phan added Truecolor support in 1996. Vincent Renardias contributed a man page, Joey Hess packaged it up for Debian, and Marius Gavrilescu re-implemented the background image feature.
When I learned xfishtank had been orphaned, I decided to adopt it, or at least give it a decent home. I've tried to reflect the history in the git log. If you know of intermediate versions not represented here, or have patches for me, please send them along to Jim Rees <firstname.lastname@example.org>.
If you'd like to help, I could use packages for various OSes.