I have coded a few plugins for BatClient. They haven't been tested on any other computer than mine because no-one volunteered, but I see no reason why they shouldn't work elsewhere. I developed them with WinXP and Java SE 6.

The URL is http://www.helsinki.fi/~tvkankaa/bat-plugins.html .

The first, and most mature one, is BatPathFinder (currently version 1.01). It basically simplifies your travels by automatically searching the lowest cost route from your current location to wherever you want to go, and then walks or sails this route. It's easy to set up and you can use the standard location names from the realm map window. If you are on the outworld, it can also automatically find where you are if you type 'map'. Basically it goes like this (if you use the command line):
map
$w digga'sdomain
$w gogo
make exp
map
$w ranger
$w gogo
spend exp

The second plugin is BatCombat. Its main purpose is to make combat easier to follow by using indentation and some ascii graphics, and it also includes a hit counter. This software is still in development and doesn't completely work as intended (especially gagging lines doesn't work well since BatClient doesn't support it yet, and there are some other issues), but I think it's still pretty good improvement over the standard combat you see, even with it's faults.

The final plugin is BatSuperLogger which was meant to be a replacement for the inbuilt logger in the BatClient, so that you could also log color codes into files, but I stopped the development when I realized that there really was no sensible way to log user typed commands ("set echo on" does work but then you have to turn it off every time you want to go 20 e non-spammily, or use that BatPathFinder plugin). It does do what it's supposed to, though, and you can sometimes edit the files with LogEdit software (sometimes LogEdit crashes).