Websheet is a project mainly written in JavaScript, it's free.
bookmarklet to make any table on the web a spreadsheet
The idea is simple, and this is an old prototype. I want to a bookmarklet that'll create a basic spreadsheet out of tables of data in the browser.
The basic implementation that exists here allows editing, but not much else. Ideally, there'd be the ability to do basic calculations with a preset list of functions, and the like.