BOINC - BOINC is an open-source software platform for computing using volunteered resources
Micro Work 4 all - New Website aiming to get more workers and job seekers to perform tiny task and make money.
Apache Mesos - Apache Mesos abstracts resources away from machines, enabling fault-tolerant and elastic distributed systems to easily be built and run effectively.
Picoworkers - Earn money from doing short, easy tasks similar to Microworkers. Picoworkers is the best alternative to Microworkers I ever find.
JPPF - The open source grid computing solution.
Amazon Mechanical Turk - The online market place for work.