Keygen - A dead-simple software licensing API built for developers
@ctivate - Activation Solutions is a software license management system solution to protect your software product from illegal copying or distribution.
Labs64 NetLicensing - Monetize your digital products and services
WebCops - With more than 30 years of experience in copy-protection and encryption. Link Data is making protection for CD, DVD, USB and web on Windows, Mac and Linux.
SoftwareKey Licensing System - SoftwareKey System is a set of software development tools that help programmers implement copy protection, license activation and management, metering, eCommerce, and business automation.
CodeMeter - License Management