ISOLDE:
A Maple package originally developed by M.A.Barkatou and E.Pfluegel for the symbolic resolution of systems of ordinary linear differential and difference equations. We recently updated it to Maple 15. Its repository is hosted on sourceforge. See also the software demo at ISSAC 2012 [pdf].
FSums:
A Mathematica package for determining inhomogeneous recurrences for nested sums over hypergeometric terms with nonstandard boundary conditions. The repository is hosted on bitbucket.
Sage:
I contributed with small fixes to the open source computer mathematics system Sage. At the moment I am implementing algorithms from ISOLDE more efficiently in Sage.