Slimefun is a relatively popular plugin that adds many advanced features to Minecraft. Some of the additions sf brings to the game include electricity, machinery, new foods, magic, and much more. Think Feed the Beast but without mods required. It accomplishes this modded-style gameplay without a mod being required by creative use of deco-heads, multiblock recipes and some trickery NBT data turning existing items into new mechanics. This is a very advanced plugin with a lot of work put into it by it’s developer. Unfortunately, mrCookieSlime has decided to leave the bukkit community to pursue other interests.
The developer has made his code available on github and changed the license to GPLv3. This creates a unique opportunity for a new developer to step in. It isn’t every day such an advanced plugin is up for grabs.
If you have an interest in plugin development or already have your own plugins and are looking for a new project slimefun is worth looking into. It would allow you to step into an already popular project with a sizable user base.
I would offer a word of caution. Slimefun, along with it's accompanying addons are big. It was quite a load for one person to carry. If you aren't sure if you have the time or energy for it, you probably don't. In fact, this project would probably be better handed by a developer with contributors. Even better would be a small team of devs.
If you are interested, take a look at the following links. Also, feel free to contact me. One of my servers is a slimefun server and, of course, I have a test server as well. I’ll be glad to help in any way I can.
Disclaimer: I do not represent mrCookieSlime, TheBusyBiscuit, or Slimefun. I have not consulted the developer previously known as mrCookieSlim before posting this. I am writing this as a concerned server own of a slimefun server who does not wish for the worst to happen, the loss of an awesome plugin that has fundamentally transformed my server as well as many others.