Trial is fully functional for 30 days. If you want to continue using Bugz after that, please buy a license. Version 2.2.4.
As a developer you need something to keep a list of outstanding issues or possible future enhancements. You can use pieces of paper, a textdocument, a spreadsheet or something like Bugzilla. Bugz is intended for those developers who need something more than simple lists, but have no need for a full blown server solution.
Mac OS X 10.9 or higher is required to run Bugz.