OpenMultiTracker is a open sourced repository for Muliple Visual Tracking. It's written in C++, high speed, easy to use, and easy to be implemented in embedded system.
For Single Object Visual Tracker, check: OpenTracker.
(not complete, tell me if I forgot you)
Simple Online and Realtime Tracking Alex Bewley, Zongyuan Ge, Lionel Ott, Fabio Ramos, Ben Upcroft