LaunchBar 6
This new version packs a lot of great new features, including a completely redesigned, themeable user interface, extensibility via custom, script–based actions, suggestions for Google and DuckDuckGo, live Calendar input feedback, new indexing rules like Emoji or Finder Tags, Info Browsing for accessing an item’s metadata and so much more.
LaunchBar has been one of my favorite apps for the entire Mac OS X era.
See also: Shawn Blanc, Adam C. Engst, David Sparks, and Kirk McElhearn.
Update (2014-07-06): There are also some great new features in 6.0.1 and 6.0.2.