TinyTuner
TinyTuner is a community developed tuning tool. I it used mainly for the series 2 L67 vehicles and adds a lot of capabilites to tuning that are not available in HPTuners or Digital Horsepower alone. To utilize this tool you will need a .bin formatted version of your tune. With DHP there is no conversion necessary, however HPTuners users will need to have their proprietary tune file converted by HPTuners.
More information can be found on the website for it located here: