More than a year ago, I needed a module which allows users to send private messages for a newly created Drupal 6 website. So I stumbled over Privatemsg. However, back then, it was an early development release which missed many features, had some bugs and so on. So I decided to help improving it.
7 weeks ago and probably hundreds of patches later (but still no stable release!), litwol made me a co-maintainer of the module which allowed me to commit patches myself.