Version 2.x uses the "old" FileMaker API for FileMaker 5 to 8.5
Version 3.x uses the "new" FileMaker API for FileMaker 7 to 9
Both versions support the exactly same functions. The only reason why we developed a version 3.x was the circumstance, that FileMaker 8.5 on INTEL Macs does not load version 2.x plug-ins.
There is no version 3.x for Windows because it is simply not necessary. Version 2.x contains the same functions as version 3.x
Our developer license allows the developer (a company or individual) to ship our plug-in with FileMaker Runtimes or FileMaker Pro bundled with the developers application. It is not limited to one site or one application. If you purchase a developer license you are allowed to distribute the plug-in with every of your applications without extra fees.