Musaios is commercial (shareware: you can try it, but eventually you may need to buy it). For a completely free TLG / PHI reader check Diogenes.
Musaios software by Darl J. Dumont and Randall M. Smith, works with the TLG CD ROM (containing Ancient and Byzantine Greek texts) and the PHI CD ROM (containing Old Latin texts). It has a convenient interface (no need to use the mouse all the time). Number of search matches is limited, and searches are rather slow. It copies only small amounts of text.
Musaios is currently available in a 32-bit native version for Windows. Development of the Macintosh version previously announced has been suspended.
Please note that to use Musaios you must first get the Thesaurus Linguae Graecae (TLG) or/and the PHI CDs. These CD ROMs are not included in Musaios. Note also that the TLG collection is now available only on-line; the CD version is not updated any more.