Alfred: it's like Quicksilver, but betterOS X alfred · quicksilver
I recently started to use Alfred, first along Quicksilver, then as a full replacement. For those of you who never used any of these two, they act like Spotlight on steroids: invoke them with a shortcut, type in a few letters, and let the fun begin. Quicksilver lets you do the basics (launch programs, open folders…) and way, way more.
A simple example? You can type a picture name, then use Quicksilver to resize it at your will, then re-invoke Quicksilver to send it to someone in your Address Book. That's already pretty impressive, but the amazing part is being able to do it all from the keyboard. Command-line gurus (and to be honest, even command-line regular users :) ) know that using the mouse is usually a waste of time.
However, Quicksilver development seemed to have stopped. Blacktree, QS developers (check out Nocturne, it's awesome!), hasn't given any sign of life for quite some time. Some development seems to be going on on GitHub, but nothing ground-breaking.
Considering I don't use most of Quicksilver's possibilities, and that I felt QS was getting slower and slower (an index-related issue maybe?), I tried Alfred.
Alfred is fast. Blazing fast. It's especially impressive on a MacBook Air, with its slow-ish processor and sluggish hard drive.
Considering I use it often to launch programs and web searches (you can add you own search engines), the speed improvement is what sold me. Check it out!