Calculix is a free and open sourcefinite element analysis application that uses a similar input format to Abaqus. It has an implicit and explicit solver (CCX) written by Guido Dhondt and a pre and post processor (CGX) written by Klaus Wittig. The original software was written for the Linux operating system. Convergent Mechanical has ported the application to the Windows operating system.
There is an active community online that provides support via a Yahoo! discussion group. Convergent Mechanical also provides installation support for their extended version of CalculiX for Windows.