Slimefun is a plugin which aims to basically turn your Bukkit Server into a modpack like FTB without installing a single mod. It offers everything you could possibly imagine. From Backpacks to Jetpacks... It also adds an API allowing you guys to easily install/code Addons for this. You own a Server which is not only minigame-based and your Players got bored of playing Survival? Then you will absolutely love this Plugin! It adds a whole new Layer of Survival to your Server by adding more than 400+ new Items!
Please use the Slimefun Guide to see how to build thigns in-game. This guide is found in the Mainmenu Item.
This youtube tutorial also helps. https://www.youtube.com/watch?v=m4BJINzkWUg