Several plugin bundled with TeamCity are developed by JetBrains and are open-sourced under Apache 2.0 license.
The plugins include:
Eclipse Integration
ClearCase VCS Support
FxCop Runner
Rake Runner
REST API
(bundled since 5.0)
plugin page
XML Test Reporting
(bundled since 4.5)
plugin page
Mercurial VCS Support
(bundled since 5.0)
plugin page
GIT VCS Support
(bundled since 5.0)
plugin page
SourceGear Vault
(bundled since TeamCity 5.1)
plugin page
Build Queue Priorities
(bundled since TeamCity 6.0)
plugin page
Swabra
(bundled since TeamCity 5.1)
plugin page
NuGet
(bundled since TeamCity 7.0)
plugin page
Agent Info
(bundled since TeamCity 7.0)
svn root: http://svn.jetbrains.org/teamcity/plugins/agent-info/trunk
PowerShell Runner
(bundled since TeamCity 6.5)
plugin page
Shared Resources
(bundled since TeamCity 8.0)
plugin page
Queue Manager
(bundled since TeamCity 8.0)
plugin page
SBT Runner
(bundled since TeamCity 9.1)
plugin page
Commit Status Publisher
(bundled since TeamCity 10.0)
plugin page
Deployer plugin
(bundled since TeamCity 10.0)
plugin page
VMware vSphere Cloud
(bundled since TeamCity 10.0)
plugin page
Investigations Auto Assigner
(bundled since TeamCity 2018.2)
plugin page