Yep, I'm 100% serious. Right now, on my phone, is an alpha, proof-of-concept build of Portal. No, it's not official (it's definitely not supported by VALVe Software in any way), but it is tantalizingly awesome. Now, before you ask, we aren't going to link to the apk - it's from a pretty sketchy source. But if you look hard enough, you'll probably be able to find it out there in some of the darker corners of the web.
If you were part of the PC gaming scene in the late 1990's and early 2000's, you almost certainly played Counter-Strike at some point. It was the online first-person shooter (of course, Doom III was around as well), and was essentially a modified runtime of Valve's popular sci-fi FPS Half-Life. Later iterations of the game like Condition Zero and Counter-Strike: Source lacked the magic which made the first game so addictive, and so the series has essentially been undergoing a slow death over the last few years.
Unfortunately, the update comes at a price, as there’s no Wi-Fi support in the current build. The reason for this is because the original kernel has been replaced to protect the identity of the source.