Synergy is the Half-Life 2 cooperative modification that enables you to play with others through Half-Life 2 and it's episodes (Episode 1 and 2), as well as our own levels.
You may also install other third-party mods, such as MINERVA: Metastasis and ROCK 24, to also play them cooperatively with other players.
Synergy tries to maintain the true Half-Life 2 gameplay, while still adding in our own unique ideas.
The documentation contains some usefull information on playing cooperatively and changes to Synergy.
We also provide some Documentation for level artists and model designers, to help make the editing experience easier. However, we do target the "Advanced Users" audience, but you are welcome to send us feedback or ask questions at any time.