Portal: Still Alive, but instead of it being a mod on your Steam library, it's a map pack you can find in Bonus Maps.
I already really enjoyed the Portal: Still Alive content, but it did bother me that the levels were separate from my main Portal install. I'm a bit of a perfectionist about things, so having it all in one area makes me happy! Thank you for making it into a map pack.
Easier to navigate then the standalone version.