Bug Tracking is an integral part of end to end software development life cycle. May it be unit testing, system integration testing or user acceptance testing, tracking bugs till closure is pivotal to successful and on time software releases.
There are many paid as well as free (open source) defect tracking tools available out there in the wild, and narrowing down to one needs a bit of research. One can track bugs using a simple spreadsheet or choose to go ahead with a feature rich bug tracking software like BugZilla, Redmine, JIRA, YouTrack, FogBugz or MantisBT.
Open source bug tracking tools like Bugzilla, MantisBT and Redmine are freely available and are used by individuals as well as large scale enterprises for bugtracking. There are companies who provide premium support at a nominal fee and take care of the initial setup, configuration, onboarding, and handle any issues later on. Basic support, however is provided by the community of developers, free of cost.