I have extended my client with a plug-in system which should allow all of you to build your own plug-ins to hook into the client (to some extent).
They are accessible under the Xtended menu (originally implemented by Ender).
Using plugins
This part is simple! You download the plug-in and place it in ~/Salem/plugins.
I am planning to maintain a list of plug-ins on this first post of which I have personally verified the source code (not guaranteeing that it will do what it says, but guaranteeing that it won't do anything nasty).
hello world pluginhttps://github.com/DonnEssime/SalemFuelPlugin/raw/master/dist/SalemFuelPlugin.jar
pickup plugin
seller plugin
frog/small kritter plugin
fuel filler plugin
distiller plugin
Creating your own plug-ins
I have tried to make this as painless as possible, but unfortunately there are quite a few steps involved.
You will find a comprehensive guide in the README of the PickupPlugin git repository.
I have (against better habits

Note that, through the "load" method, it is also possible for plug-ins to permanently influence client behaviour without ever being activated once.
Your turn
Now it's up to you!
Some extensions to my client I will make accessible as plug-ins rather than as full-fledged client extensions, depending on where they best fit. One hopeful dream is to, one day, have some kind of central plug-in list and a full updater GUI for both the client and any and all plug-ins you may enjoy. One day.