Quicksilver

The popular definition "what Spotlight should have looked like" is nicely understated, if not outright false. QS is much more than a tool to index content: it turns complex productivity routines into simple motor patterns. I could hardly imagine working without QuickSilver and I learn every day new ways of adapting it to my needs. I am just so grateful I came across this piece of software. The source code is released under the Apache License since Nov 2007, which is yet another reason to love this tool.