One of my absolute favorite tools on OS X is LaunchBar. LaunchBar is always the first application I install on any OS X system -- it is such a productivity booster that without it I feel lost. LaunchBar is a powerful tool with a lot of uses, but if I had to describe it in two words it would be "application launcher" or "system searcher."
LaunchBar sits inconspicuously in the background until you need it, much like Spotlight. It is a searching tool, somewhat like Spotlight, and is activated in a similar manner. (In fact, I routinely reassign Spotlight's activation keys to [CTRL]+[OPTION]+[CMD]+[SPACE] since it is used so rarely, and let LaunchBar activate with [CMD]+[SPACE] which is Spotlight's default).
When activated, LaunchBar pulls down from the menu bar -- unobtrusive and out of the way. Begin typing and LaunchBar starts searching for items that contain those same letters. For instance, to launch Safari, type "sa" and LaunchBar will have highlighted it. If the match isn't correct, use the arrow keys to select the item you want and press enter to launch it. LaunchBar trains itself and remembers what you most often select when typing in letters, so if you typed "sa" and routinely picked "Server Admin" you will find that Server Admin will move to the top of the list, before Safari.
Likewise, if you want to assign a shortcut to something, use LaunchBar to find it, and instead of pressing enter, right-click on the item in the list you want and select Assign Abbreviation from the list. In this way, I assigned the abbreviation "stt" to launch my "Safari-to-THL.scpt" AppleScript.
But LaunchBar does more than just search for things and launch them. Activate LaunchBar and start typing numbers and you have a full-featured calculator available. Activate LaunchBar, type tex to find TextEdit (or TextMate, etc.) and then press the space bar or the right arrow to look at a list of files that the application has recently opened. Use the arrows to find the file and press enter and that file will open in the appropriate application.
Want LaunchBar to act as a filesystem navigator? Activate and press "~" and use the arrow keys to navigate your home directory. If you find the file you want, press enter and it will open in the default application for that type. To do the same with the boot volume, use "/" instead of "~". Want to search your Safari history or bookmarks? LaunchBar can do that too.
LaunchBar Clipboard manager
The new version of LaunchBar, version 5 (currently in release candidate status) adds a number of really nice new features. One of these is a clipboard manager. In the LaunchBar preferences, select the Clipboard icon and enable Clipboard History. You set a number of defaults including whether or not LaunchBar will remember history across reboots and how many clipboard items to remember. Assign a keyboard shortcut (I use [OPTION]+[CMD]+[\]) and it will display the defined number of items in the clipboard, showing the first line of multi-line entries. You can use the arrow key to dig into an entry to see all of the lines and if you hit enter on one of these lines, it will be displayed in large on the screen. If you select the entry itself, it will paste it into whatever application you were using when you activated LaunchBar.
Control your search results with customization
Finally, LaunchBar allows you to have fine control over what you want it to present in search results. By activating LaunchBar and then selecting the Index - Show Index option from the menubar you can fully customize what LaunchBar returns in search results. If you want it to search through Address Book entries, calendars, browser histories, and bookmarks, you just enable them. If you don't want it to search your iTunes library and don't need it to index unix executables, exclude them. LaunchBar will only return results from criteria that you want -- and ignores those you don't. Here, as well, you can create and modify search templates. For example, you can have LaunchBar activate, type "wik" and press enter and whatever you type in the provided text field will launch as a query to Wikipedia in your default browser.
Ultimate productivity tool
I could keep going, but I think you get the idea. LaunchBar is a veritable Swiss Army knife utility with more productivity tools than you can shake a stick at. There is so much more that LaunchBar can do, and so many ways you can customize it to your particular needs. For instance, you can use LaunchBar to launch AppleScripts automatically and seamlessly for you. Remember the "Safari-to-THL.scpt" abbreviation I noted above? By activating LaunchBar and typing "stt" and hitting enter, I send the name and URL of the foremost Safari window as an inbox item to The Hit List. There is no interaction or prompting or clicking or dragging and dropping required, just a few swift keyboard commands. LaunchBar is my ultimate productivity booster.
Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.