Taken from the site:
Since all planned development for our Half-Life 1 release is complete, MechMod has now been converted into an inactive and opensource project. The purpose of this change is to allow new community modders and programmers to learn from what we have done. The open source movement/initiative is truly resourceful towards the online community and helps aspiring programmers learn from other people's projects. As of 23 July 2006, the source-code for MechMod Alpha is freely available for everyone to download under the Open Source License. Another license to consider and follow is the Valve Half-Life SDK EULA as MechMod is a game which is based on Half-Life's engine/SDK.
Please read the following documents before continuing:
Open Source License, version 3.0:
External Link, SourceForge Document
Valve Half-Life SDK End User License Agreement:
Eternal Link, SourceForge Document
Be Sure to visit their site too.