We'll OpenKM source code and community edition is under GPL and is totally free, that's correct.
There's a supported version by us - OpenKM enterprise edition - ( Community version is only supported by it forum and community users help ) which some extra enhancements like Workflow, extra tunning and OCR configuration, etc...
If you take a look at Features web section (http://www.openkm.com/Features.html) you can see marked as "*" the differences between community and enterprise version.
I think we'll need to do a features version table no, to show it better ?