Confluence

Confluence is a web-based corporate wiki written in Java and mainly used in corporate environments. It is developed and marketed by Atlassian Software Systems. Confluence is sold as either on-premise software or as a hosted solution. Its license is proprietary, but a zero-cost license program is available for non-profit organizations and open source projects.

Source: Wikipedia.

Main site - http://www.atlassian.com/software/confluence/