Portal: Combined Technologies mod

The mod takes place during the Portal 1 era in 2 alternate universes. The first is where the player character has been held in stasis for a while and has lived in, and the other is a world where the combine from Half-Life 2 have taken over Aperture in hopes of finding portal technology they can put to use. As a result, Aperture begins slowing down testing completion rates, while testing more subjects than ever in an effort to deny the combine their portal technology. In the heart of Aperture's new facility located above a gold mine in California, there is a massive dark energy reactor hooked up to a central chamber, where the combine promise to house a powerful supercomputer using Cave Johnson's assistant as a brain.

You are sent to this universe by a mistake in the multiverse device back on your prime earth, which spirals down into a large endeavor to safely travel back to your universe, and in doing so, bring chaos and disruption to an aggressive force attempting to secure their role over the citizens of that universe.