Im looking for a knowledge base/wiki/FAQ system that fits these criteria:
- Written in PHP
- Rich text editing (rather than markdown)
- Has search functionality
- In general, user friendly, easy for non technical people to use
My Synology NAS provides add-on packages. One of them looks like it would be appropriate for your needs.
DokuWiki is free and runs on multiple OS. It seems to tick all of your requirements. As far as being user friendly and easy, that’s subjective. You’ll need to decide by downloading and testing it.