Is there knowledge-tree document management alternative based on php and MySQL for self-hosted Knowledge management apps?
Not sure if this helps you or not since like knowledge-tree, MindTouch TCS is a cloud-based business solution. It is an extremely flexible knowledge base created with keeping teams of business professionals in mind with it's WYSIWYG editor. The desktop connector helps you manage and import your Microsoft Office documents --- so no new tools to learn. :)
If you really need a self-hosted solution you may want to look into MindTouch Platform. It doesn't have the useful knowledge base features such as self organizing content. It is, however, still a great way for teams to collaborate and you can still use the desktop connector for your Office docs. And there is a free trial.
Best of luck to you!
What kind of documentation do you need it for? Internal as in an intranet? External as in help docs?
I've never heard of knowledgetree, but I'd have to agree with paintturtle. We used their free open source core product for our intranet at my old company and we're just starting to use their TCS "social knowledge base" for our help documentation where I am now.