Just to clarify the requirement:

A TAB package should provide the following, in addition to abc import/export and MIDI output

Mandatory
Selectable number of strings
Specification of tuning of each string

Desirable
Tab and notation staffs both visible, and aligned
Onscreen edit of tab items automatically updates score and vice versa
Audio Implementation of Hammers and Pulls
Aligned lyrics

Optional
Chord dictionary (dynamic, dependent on string tuning)