BOINC - BOINC is an open-source software platform for computing using volunteered resources
Jenkins - Jenkins is an open-source continuous integration server with 300+ plugins to support all kinds of software development
Apache Mesos - Apache Mesos abstracts resources away from machines, enabling fault-tolerant and elastic distributed systems to easily be built and run effectively.
CircleCI - CircleCI gives web developers powerful Continuous Integration and Deployment with easy setup and maintenance.
JPPF - The open source grid computing solution.
Travis CI - Focus on writing code. Let Travis CI take care of running your tests and deploying your apps.