This is Forge Mod Loader.

You can find the source code at all times at https://github.com/MinecraftForge/FML

This minecraft mod is a clean open source implementation of a mod loader for
minecraft servers, minecraft bukkit servers, and minecraft clients.

The code is authored by cpw.

It implements API defined by the client side ModLoader, authored by Risugami.
http://www.minecraftforum.net/topic/75440-

It also contains suggestions and hints from LexManos, author of MinecraftForge.
http://www.minecraftforge.net/

Additionally, it contains an implementation of topological sort based on that 
published at http://keithschwarz.com/interesting/code/?dir=topological-sort

It also contains code from the Maven project for performing versioned dependency
resolution. http://maven.apache.org/

Forge Mod Loader downloads components from the Minecraft Coder Pack
(http://mcp.ocean-labs.de/index.php/Main_Page) with kind permission from the MCP team.