What tools do folks use to actively track bugs?  I've been using
GNATS for ~25 years (so have a large "history file" for my various
projects, over the years).

Presently, I release incremental "dumps" of pertinent portions
to folks who are leeching off my codebase (no real-time access
to my sources remotely -- nor is there a desire for same!) so
they can see what's been uncovered and repaired (to further
clarify changes in the regression testing suites).  GNATS dump
corresponds with codebase dump ("dot" release).

Aside from "reminders" to myself regarding what I've found, how
I found it, how I fixed it and a cumulative history file, I
mainly use it to track "bug rate", over time, as a crude
predictor of "bugs remaining".  (does anyone else do this?)

[Bugs don't linger in the codebase; when discovered, they're
usually promptly repaired so there's little need to query
the DB for "outstanding" bugs nor assign responsibility for
fixing same.]

My primary repo is CVS-based (again, more than 25 years of
history therein -- no, I'm not keen on converting it to
a newer VCS as CVS fits my needs adequately).  I don't see
much need/appeal to integrate bug tracking with the VCS.

GNATS has been a win because it just catalogs my discoveries
without getting in the way of my other tools/process.  But,
I'll be developing "user-level" apps, soon, and those will
be more "exposed", going forward (i.e., maintained by users),
so a more current tool may be appropriate.