What is the easiest wiki engine to use?

Question

Wiki engines

There is a team of 7 people to support and refine the product.
There are no product docs.
We are taking notes on key issues on our own, but I want to combine all this into a wiki.
Requirements:
1. It must be technically possible to keep it and synchronize it between users through a cloud service without losing functionality.
2. Zero entry threshold. It is advisable not to install any software other than a browser to read and write.
If these are fantastic requirements, then at least get as close to them as possible.
Thanks
UPD:
The first answers suggested below assume PHP is installed on the machine.
I understand that a serverless wiki is a fantasy, but I assumed that suddenly there is something written in pure JS, for example (you never know, there are a dime a dozen geniuses in the world). If there is no such thing, then it means as it is) The main task is to put a person behind the car, he makes a couple of clicks, and he has a wiki! In the Word somehow reluctance.
UPD2:
Found: MDWiki. Powered by JS, reads markdown files. Not sure if this will be handy, but the current issue is closed.

Answer 1

DokuWiki, MediaWiki

Answer 2

The easiest free wiki to install is perhaps DokuWiki, the most user friendly XWiki is a second generation wiki written in Java, LGPL distribution license, functionality includes a blog, API tools, comments, LDAP authentication, export pages to PDF. There is also the possibility of programming scripts (Velocity, Groovy, Python, Ruby and PHP) and support for the syntax of popular Wiki engines (Confluence, JSPWiki, Creole, MediaWiki, and TWiki), WYSIWYG editor, integration with office (Openoffice / Labraoffice). Used by many companies around the world. 25 interface languages, including Russian. Of the minuses - very little technical documentation in Russian.