Nearly 15 years later, Valve's thrown a Half-Life 1 modding team a bone - Sven Co-op is to become a free, standalone game.
The team has the go-ahead to work on a custom version of the Half-Life engine for its co-op-enabling - and much more - mod. The entire Half-Life campaign (tweaked for two-person co-op) will be thrown in for free, so you won't need to buy any other Half-Life games in order to play (as you do now).
SteamPipe integration means updates will be swifter, and complete control over the engine means the game will be better all round.
"We're looking forward to working with one of the greatest game engines ever made, and we can assure everyone that there are many, many more updates to come."