The offical repository of Reliquary! That mod, with the magical swag, and a weapon, and stuff.
Originally made by x3n0ph0b3, Reliquary is now developed by both TheMike and x3n0ph0b3.
We use ForgeGradle. There are instructions inside the 'build.gradle' file in this repository.
Every major version increase means a Minecraft version increase. 1.1.x is for 1.6.4. 1.2.x will be for Minecraft 1.7. 1.3 will be for Minecraft 1.8. And so on.
The licence is located at COPYING.txt, but to save you the trouble, it's GPLv3 (with one of the sounds under CC Attribution License).
Basically, do whatever you want, as long as it's free, open source, and stays under GPL. (Yes, that allows you to use it in your modpack.)