yafu
Automated integer factorization
...Most algorithm implementations are multi-threaded, allowing YAFU to fully utilize multi- or many-core processors (including SNFS, GNFS, SIQS, and ECM).
YAFU is primarily a command-line driven tool. You provide the number to factor and, via screen output and log files, YAFU will provide you the factors. There is also an interactive environment similar to MATLAB or PARI/GP, where you can type commands and store results.