The API reference docs for GadgeteerCore are provided here in HTML format. Your Gadgeteer mainboard and modules will also come with documentation that describes how to use them.
If you're looking for general information on Gadgeteer, check out What is Gadgeteer? and Get Started.
Latest Stable Version
This is the latest released version of GadgeteerCore. There are slight differences between GadgeteerCore running on NETMF 4.1 and running on NETMF 4.2. Please refer to the version corresponding to what you run on your mainboard.
The source code for this release can be found at http://gadgeteer.codeplex.com/SourceControl/changeset/changes/17974.