[edit: No way in hell will I use something that grabs system access like this.]
Gears is an open source project that enables more powerful web applications, by adding new features to your web browser.
2011-03-11 it was thankfully abandoned.
I had already known of it, but WordPress has a mention of it in
Tools > Tools in its control panel (http://yourblog.wordpress.com/wp-admin/tools.php) and said it would speed up surfing.
So I decided to check it out. Wow, it's installed as a Firefox extension. Win.
Well.. so far so good.