FastSum is integrity checker software based on MD5 checksum algorithm. It is a console and GUI, freeware / shareware application for Windows platform. FastSum was first released by Kirill Zinov and Vitaly Rogotzevich in 2003 as a freeware console application. Eventually, the original version was renamed to the Command-Line Edition and expanded with graphical user interface to the Standard Edition and released as shareware. Today there are both freeware and shareware versions available.