My Software: 
Sage  contains implementations of most modular forms algorithms; I initially started this project to provide an open source home for modular forms software.


HECKE: Modular forms calculator  I haven't changed this in over 10 years!


Source code for my MAGMA modular forms packages
(these are included with MAGMA)


A GP/PARI Hecke operators calculator
 very old (unchanged for over 10 years) and very slow, but easy to change if you
an expert with PARI.


Hijikata trace formula

 
Other People's: 
Verrill's fundamental domain drawer (local mirror)


Peter Green's Heegner Points Package  Sage now has better code for computing Heegner points
(local mirror)


Qing Liu's Genus Two Reduction (local mirror)  this is included in Sage now via the genus2reduction command.


ComputeL  Computing special values of Lfunctions by Tim Dokchitser
(local mirror)  this is also in Sage.
