Firefly (previously known as the PC GAMESS) is a freely available ab initio and DFT computational chemistry program developed to offer high performance on Intel-compatible x86, AMD64, and EM64T processors. ... At moment, Firefly includes no more than 5% of the legacy code. ... Firefly is freely available for all main PC operating systems: Windows, Linux, and Mac OS X. Firefly supports various Windows versions including Windows 8, Windows 7, Windows Server 2008, Vista, 2003, XP, 2000, NT, and 98/Me. ...