I've got a lot of good info from these forums so I though I should contribute something back and here it is. Ok - this doesn't have any fancy gauges, bar graphs or charts but hopefully it is a good starting point for someone who wants to write their own obd-ii software be it gauges, logging or whatever you prefer.
It will interpret a few of the common OBD-II commands: rpm, vss, etc and will display you the raw binary (hex) data for the rest. This project is open source and should work with any elm or compatible obd-ii interface. It was written with C# express 2008, so you will need the .net Framework.
If you don't have an elm interface there are schematics in the
elm datasheet from elm electronics.
You can download the source (there are compile windows binarys in the /bin directory of the zip) from the
Binary Construct sourceforge page. If I do updates, etc they will be on sourceforge or my website
http://www.binaryconstruct.com.
I hope you find this useful and best of luck programming.