Adding a textbox that visitors can edit

Hi,

I’ve searching now quite extensively a way to incorporate a simple textbox in the front end that could be edited by page visitors that retains the earlier content. Basically something that would have editable text area and save changes button. Bit like a Google document where users could collaboratively edit the content. I keep thinking that easy way to do this exists, but I just can’t find it.

Thank you in advance.