How can I build a website with fields that any visitor can edit?

I'd like to build a website which has the following features:

• There should be a few fields which store numerical values.
• These fields should be editable by anyone who visits the site

A second order feature which would be nice, but isn't necessary

• It would be nice if when multiple people are visiting the site and one visitor updates a value, the webpage reloads for all visitors once the value is saved, updating the value seen for all users

How would I go about implementing the above?

I'm not sure what terms I should even be googling to approach this question, so any advice is appreciated.