Semaphore is a hosted continuous integration and deployment service used for testing and deploying software projects hosted on GitHub and BitBucket. While open source projects can use Semaphore for free in its full capacity, free use for private projects is limited to 100 builds per month (Semaphore Classic) or $20 of service every month (Semaphore 2.0).One of Semaphore’s features is native Docker support, which enables testing and deploying Docker-based applications.