[Hephos]

With ScapeFX you can build and code your own custom mud client with a powerful underlying codebase. ScapeFX is crossplatform and work on Win, Mac and Unix. ScapeFX is FREE for both commercial and non-commercial muds!

You build your client using "real" Java in your preferred IDE. I recommend Eclipse: Eclipse - The Eclipse Foundation open source community website. or NetBeans: Welcome to NetBeans No silly "scripting" the UI or similar. Use the full power of the complete Java API to customize your client.

Here is a sample java project to use as a reference:
SampleProject - ScapeFX Wiki

ScapeFX supports skinning by easily changing images and also building your own Skin plugin:
Skin - ScapeFX Wiki

Use the SFXP protocol to enhance your game, or why not use your OWN protocol?
SFXP - ScapeFX Wiki

Some sample plugins:
SamplePlugins - ScapeFX Wiki

And check out the Sharune client 'Firebolt' (ScapeFX implementation) here: Sharune Multi-User Dungeon