CVSNT is an open-source version control system.
CVSNT is a client–server version control system compatible with and originally based on CVS (Concurrent Versions System), which has become popular in the open-source world.
Users unhappy with the limitations of CVS (in 1998) began the development of CVSNT. The original limitations addressed were related to running CVS server on Windows and handling filenames for case-insensitive platforms.
To many people CVSNT is best known because it has been embedded in a 3rd party systems such as TortoiseCVS or WinCVS.
The status of the project is active, with further releases of CVSNT 2.5 planned, and continuing evolution of CVSNT/EVS 3.1. CVSNT/EVS will implement a complete SQL database repository to support further complex server and client features.
More information is available on Wikipedia's CVSNT article.