One common application of mouse chording, called rocker navigation, is found in Opera and in mouse gesture extensions for Mozilla Firefox.
Rocker navigation typically involves the following two mouse chords: The operating systems Plan 9 and Oberon and the acme development environment make heavy use of mouse chording.
OS/2 Presentation Manager can also use chording to copy and paste text using two buttons however Common User Access key combinations are more frequently used.
A similar feature such as a context menu would require less training.
[1] This does not enable chords which involve the middle click.