Tidbit
In November 2013, Jeremy Rubin, a 19-year-old MIT student, developed a JavaScript program called Tidbit. This program was a concept/pilot, but the idea behind it was to use JavaScript to mine for Bitcoins.
It was thought as a replacement for advertisements. Instead of being overwhelmed by ads, a user visiting a site using this script would lend part of their processor cycles to mine for Bitcoins while surfing on the site.