Genius is one of the oldest GNOME projects, it has been the original GNOME calculator before I got wild ideas about it doing absolutely everything. It is programmable has a powerful language and handles many fun features including matlab like support for matrices. It requires GNOME2 (at least glib2 if you don't want a GUI) and a recent enough gmp library. However you can still use the command line version if you prefer non-gui interface.
There is still a lot of work required to make this all nice, mostly it needs to have the function library improved and verified to be correct and documentation needs to be written (the complete help system is not yet in place). Feel free to help out
Here are the news in 0.6.1:
* On undefined identifier error, genius gives you close suggestions
* Black on white mode for the console for those that can't see white on black so well.
* More UTF-8 cleanup so other languages shoulkd work now
* More fun with font sizes and try to normally deduce the font size for the console from the theme font size on startup. Also don't write the font as a preference until it's explicitly set
* Accept file drops and open those files
* Use gnome-vfs for opening and saving files (not for load and run yet)
* Mime stuff so that you can open .gel files from nautilus
* Somewhat nicer display of real fractions
* New functions: cis
* The functions promised in 0.6.0 weren't actually added, this affects: Argument, arg, Arg, MoebiusDiskMapping, MoebiusMapping, MoebiusMappingInftyToOne, MoebiusMappingInftyToZero, MoebiusMappingInftyToInfty.
* When we complain about uninitialized functions/variables, give suggestions
* Fix "number string"
* Some code cleanup
* MacOSX install instructions in INSTALL.MacOSX (Linc Davis)
* Other minor fixes
* Translation updates (Gustavo Maciel Dias Vieira, Raphael Higino, Jordi Mallach, Xavier Conde Rueda, Miloslav Trmac, Vincent van Adrighem, Tino Meinen, Adam Weinberger, Gareth Owen, Gustavo Noronha Silva)