FluentTc - C# library for TeamCity REST API and also interacting with TeamCity within the build script
- JSON API - API to emulate Hudson's JSON one, e.g. usable for XFD. See also TeamCity's bundled REST API
- PyTeamCity - Python interface to the TeamCity REST API
- Ruby REST client - a Ruby wrapper for the TeamCity Rest API
- Sharp2City - a .Net API for the TeamCity REST API (announcement)
- SwiftCity - TeamCity REST API client in Swift
- TeamCityCLI - CLI for TeamCity REST API
- TeamCitySharp - a .NET Library to access TeamCity via the REST API (newer take).