Yesterday OSTicket 1.7 Release Candidate 2 (RC2) became available. Here is what the devs mentioned in the WHATS NEW:
* Bug fixes from rc1
* Nested help topics support
OSTicket is a popular [free] open source trouble ticketing system built on MySQL/PHP.
You can get the latest RC version over at Github. As a reminder this version is for developers and enthusiasts only and should never be used for a production environment.
source: OSTicket.com Forums