Is the most popular userscript manager for Google Chrome. Userscripts are little computer programs that for example add a download button to the YouTube page, cleanup your Facebook timeline or help playing an online game.
https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldmpobfkfo
https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldmpobfkfo