BugSack eases the process of capturing bugs. It captures information about Lua errors that occurred during your play session, including the full debug stack. It aims to be invaluable to developers, and a useful tool for advanced players that use beta-quality addons.
BugSack includes a LDB data broker plugin that displays the last 5 errors in the tooltip. It can also bring up a frame to display all other errors for the current session, or for any other session. The text of the error can then be copied & pasted to a source outside of WoW (for example the forums) so that other developers can determine what's at fault.
Remember to file a ticket if you find a problem or want to request a feature.
This addon REQUIRESBugGrabber, which is the addon that actually grabs the bugs. !BugGrabber is intentionally kept small, and it does not use any libraries, to make sure that any errors in those libraries do not mess up the system.