Portal Stories: Mel is a lovely-looking community-made mod for Portal 2 that's due out sometime in Q1 2015, according to the title's store page.
The lengthy 20+ level mod will feature a new protagonist called (you guessed it) Mel, who will be partnered up with an all-new personality core and will ultimately face off against a "new, still unknown threat."
The mod will also feature custom story and dialogue, as well as new models, textures, animations and a really nifty-looking '70s version of the Portal gun. Once released, the mod will be free for all owners of Portal 2.
After seeing this trailer all I want to do is play through the base game again using that adorably clunky-looking '70s Portal gun!