Master1398s Signature has the only way to make more NPC factions currently.
Are you looking to create a third party tool or something that actually extends the game.
Megacrafter127 makes most of the third party tools that exists and he uses Java
Server Wrappers are written in different languages based on what the creator is familiar with.
To write code you need something like Microsoft Visual Studios or another program such as Eclipse...
[DOUBLEPOST=1437399759,1437399645][/DOUBLEPOST]If you don't want to write code you can modify the game with new blocks or textures as well. In that case you will be using the Block Editor Tool in the second launcher when starting the game. You would also probably make a custom config for the game by editing the config file with any text editing software.