There had been some Half-Life tech demos on the Unreal Engine 4 but none of them had a full playable (fanbased or modded) game under that engine yet.
And now Project Borealis is going to make that happen, with or without Valve's assistance. (Don't say Half-Life 3 on Unreal Engine 4 just yet.) Too bad Valve isn't going to make a game under the Unreal Engine 4, and not much news on making new games under their Source Engine 2.
Well PB has a Reddit forum for now: https://www.reddit.c...eamsofhalflife3
The FAQs has some info: https://www.reddit.c...ife3/wiki/index
Its latest update now has the un-official canon story halfway done: http://www.pcgamer.c...look-incredible
If the project goes well, I'll pay for a retail game like this with a polished engine, graphics and gameplay.