GlotPress is the software that powers translations for WordPress, and now also themes and plugins. It was originally written on top of BackPress (which has seen some recent revival of interest).
There have been a number of discussions about the possibility of rewriting it as a plugin over the years, including one by project lead Marko Heijnen. Yesterday, Andrew Nacin made a commit to the project to begin the process of actually converting the software.
With the progression of translation and internationalisation efforts across the WordPress ecosystem recently, this seems like a very positive move in general. I'm looking forward to seeing the project move further in this direction over the next little while.