TabIt is a Windows application that is described on its website as
a full-featured program for creating, playing, and printing guitar, bass, or banjo tablature.
TabIt is sold by GTAB Software.
The latest version of TabIt, version 2.03, was released in 2006.
TabIt is effectively abandonware.
Description of the .tbt Tabit file format
A C++ parser and MIDI converter for .tbt TabIt files
Description of the .mid MIDI file format