SkyBill is a java TCP Biller written by Doc Flabby. The latest trunk (3.0.1) "has a number of critical bugs I need to fix" [removed emphasis].   The developer hasn't posted any additional releases since May 2007 .
ALPHA - missing many key features. To get it to work you will
- you require java 5.0
- mysql is also need
- Allows billers to connect using TCP with the correct password
- Banner saving and retrieval
- passwords are stored with future-proof sha-512 (should be good for at least 10 years)
- remote messaging between servers
- basic squad support
Features it missing:
- chat support
- full squad support
- ban support
- comes with mysql connector http://dev.mysql.com/downloads/connector/j/5.0.html
SkyBill v0.11 
- Basic Squad Support Added
SkyBill v0.2 
Due to problems with the original design skybill has been totally rewritten.
The new design (more event based now) makes is a lot easier to extend, it features a module/plugin system.
This current version includes the minimum modules to run a biller.
It does NO authentication of any kind. It has no database either. It allows everyone to connect.
SkyBill v0.3 
All you need is java runtime 5 or higher
- Current does NO player or biller authentication
- Anyone can connect with any name.
- Still need to create player commands plugin
- Chats are fully implemented
- Unlimited number of chats allowed!
SkyBill v3.0.1 
DO NOT USE THIS BILLER IT HAS A NUMBER OF CRITICAL BUGS
- Features player and optional zone auth
- supports squads and unlimited chats