I checked the GitHub to work out what rr is:

rr is a lightweight tool for recording and replaying execution of applications (trees of processes and threads). More information about the project, including instructions on how to install, run, and build rr, is at http://rr-project.org.

http://rr-project.org in case you wondered

rr is my goto debugger. It opens up new super-powers for debugging scripts. Consider this gdb script:

  b broken_1_in_1000_times_at_random.cpp:1
  c
  b usually_runs_normally.cpp:1
  reverse-continue

And now step through forward to figure out what went wrong. This tool is worth your time to learn. There are a couple of minor annoyances (you can't re-use existing gdb scripts that contain the "run" command because the inferior is already running, but there are workarounds. Here's what I use:

  python
  import gdb
  class MyRunOrContinue (gdb.Command):
      """Run inferior if not already running, otherwise continue (useful for rr)."""

      def __init__ (self):
          super (MyRunOrContinue, self).__init__ ("just-go", gdb.COMMAND_USER)

      def invoke (self, arg, from_tty):
          if gdb.selected_inferior().pid != 0:
              gdb.execute('continue')
          else:
              gdb.execute('run')

  MyRunOrContinue()
  end

There are a few other minor annoyances, but all in all a great tool.