distributed.net is a loosely knit group of computer users from all of the world that is taking up challenges requiring lots of computing power (most notably the RC5, DES, and OGR cracking contests). It is simple to participate in the challenges by downloading and running their client software (which uses idle CPU time to complete its tasks).
Calcoo is a scientific calculator designed to provide maximum usability. Its features bitmapped button labels and display digits to improve readability, no double-function buttons, undo/redo buttons, copy/paste interaction with the clipboard, both RPN and algebraic modes, two memory registers with displays, displays for Y, Z, and T registers, and tick marks to separate thousands. Calcoo is written in C using the GTK+ widget library (v.2.2+).
TRIP is a general computer algebra system dedicated to celestial mechanics. It includes a numerical kernel and has interfaces to gnuplot and xmgrace. Computations can be performed with double, quadruple, or multi-precision. Users can dynamically load external libraries written in C, C++, or Fortran. Parallel computations on multivariate polynomials can be performed.