Besides the fact that the client has a very powerful scripting language, with what You can use to create and implement your own plugins with Java (as .jar packages) to the Batclient. This feature was enabled with the release of v1.53. Example here (.zip, 511kB)
batUtils uber-batUtils-1.2.jar -plugin (full version, 12-Oct-2013 | Glaurung)
Description: Plugin formerly known as batMap has been renamed as batUtils now with the addition of the corpsehandler. This replaces any version of the batMap plugin. Place this .jar under the Batclient /plugins -directory and restart client. Then issue the command "set client_mapper_toggle on" in-game for the mapping to work. See builtin manual for more information.
Newest features: Area view & search, more colours, bugfixes.
batMap Reload script -script (12-Jun-2013 | Glaurung)
Description: With this script file, you can reload the batUtil plugin window if you accidentally close it by typing: $batMapReload.reload on the commandline. Save this file batclient/scripts directory.
Prot tracking trigs prots.bcs (full version | Era)
Combat round actions rounds.bcs (ready trig | Era)
Print analyse results, dcrit/essence/etc. mage_analyse.bcs (ready trig | Wermine)
Spellnames added spellnames.bcs (full version | Dazzt)
Liting triggers lite.bcs (beta version | Era)
Some gagged lines gag.bcs (sample version | Era)
Combat Damage Analyzer cda.bcs (sample version | Glaurung)
Player Uncon trigger uncon.bcs (sample version | Glaurung) Description: Simple uncon trigger, reports player uncon and makes a command that you can use to revive, make sure to edit the skill/spell you use to it.
BatWiki Lookup script wiki.bcs (sample version | Tugmeno)
* Add these to the C:\Documents and Settings\%username%\batclient\scripts (or equivalent) -directory. Then either restart Batclient or give the /scriptreload and /scriptbootup -commands.
You can find it here.
Userland plugins will be added to this page per request.