TWiki is a Open Source Wiki especially designed for use in corporate environments. In my company I am running the new Version 4.0 as a platform for documentation by IT and R&E departments. 4.0 is a major step ahead offering improved usability and much easier installation. A WYSIWYG Editor can be activated but is still labeled as development beta. The Security-Release 4.0.2 should be out in the next days, so in case you want to give TWiki it a try, better wait for the launch. Have a look at the features or compare it to the major competitors. From my point of view TWiki is first choice for large companies. An alternative could be Confluence, but it is not under an opensource license.