I went over the different CMS that won or became runners up in each category to check who uses TinyMCE. I downloaded the package or checked their online demo to verify.

Most Promising Open Source CMS Category

ImpressCMS – TinyMCE included by default.

Pixie – TinyMCE included by default.

Pligg – Not included, integration instructions exists, seems they have no default editor?

Best Open Source PHP CMS

Drupal – TinyMCE is a downloadable module (everything in Drupal is modules), seems to be extremely popular.

WordPress – TinyMCE included by default.

Joomla – TinyMCE included by default.

Best Other Open Source CMS

Plone – TinyMCE included by default in upcoming release.

dotCMS – TinyMCE included by default.

mojoPortal – TinyMCE included but also other editors, not known if it is turned on by default or not.

UPDATE:

Overall best Open Source CMS

This category was announced after I made this post.

WordPress – Already mentioned above.

SilverStripe – TinyMCE included by default.

MODx – TinyMCE included by default.

Source website: http://www.packtpub.com/award

Out of 11 different Open Source CMS, TinyMCE is included by default in 9 of them! If you make the same check towards commercial CMS you would probably find a similar figure. The download figures for TinyMCE on Sourceforge pales in comparison with the figures these different Open Source CMS has.

TinyMCE is without doubt the most used WYSIWYG editor out there, thank you all for that.