Kenbuster - www.kenbuster.co.uk
This is a startup company who use GPS to detect whether your car has entered the congestion zone and if it has it pays the congestion charge for you.
On the server there is a java process listening on a socket, this reads messages from the GPS units and puts them in a file. Another process reads from the file, checks whether the location of the unit is inside the congestion zone. If it is it creates a payment, otherwise it just records the journey information in the database.
I created a tool written in java, using SWT for the GUI. It communicates with the database on the server via J2EE and JBoss. The user of this tool can maintain client information, make payments - using SWT Browser to fill in the congestion charge payment web page automatically , view Journeys - in summary, but with the ability to view the actual journeys on google Maps - so that the journey can be checked.
There's also a job which sends confirmation emails and sms texts automatically - the sms texts being sent via a gprs modem to save money.
I wrote all of this, implemented and tested it, and now it has been running live for a year - I still support the system.