Many of the internal projects used by SKM are distributed with an open source license.
SKM Wiki Engine
A wiki engine used to render pages at help.skmapp.com.
SKGL (Serial Key Generating Library)
A free and open source licensing system, which was one of the building block behind SKM.
Licensing Systems Article
This articles describes various license key algorithms and how they can be implemented.
SKM Client API
This is the client binaries that are used to talk to SKM.