http://release.blackmesasource.com/
The project that's spanned more than half a decade, bringing the original Valve's
Half-Life updated with Source engine graphics, new music, sounds, animations etc. tech babble as a fan project...
Finally here, to download and play
for free! Half-Life for me was one of those groundbreaking games, better than HL2 and more rememberable, played on a friend's comp as a kid when we couldn't afford one. Now it's back, in an all-new glory.
All you need to play it is Steam and the Source SDK 2007, which you can download from Steam under Library --> Tools --> SDK 2007.
And there you go. Two game threads today, but hey, legendary games they are. Enjoy.
Prepare for unforeseen consequences.