Alfred, Butler, LaunchBar, and Quicksilver display and open most of the same data types as Spotlight, but offer much more configurability. For example, you can ask them to look at only specific files or folders, or perform specialized Web searches for, say, Twitter users or IMDB entries. All except Butler also have mechanisms for adding plugins in order to extend searches to include items such as 1Password logins and Transmit favorites.
All the launchers become smarter as you use them. For example, if you type "m" in an effort to find and open Messages, perhaps Mail comes up on the list sooner, so you arrow down to Messages instead. But the next time you type "m" (or, depending on the launcher, after a few tries), Messages comes up as the first choice.
However, Spotlight always groups categories as defined in its preferences. So if you have apps listed first, then no matter how many times you select "Many Merry Monkeys.docx" as your choice after typing "m," it'll still be listed lower, among the documents.
Although Spotlight has many talents, it lacks several key features most of the other launchers have. All the rest can run AppleScripts (not just open them in Script Editor), track your clipboard history and paste previous clipboards, and control iTunes (for example, pause or resume playback). Spotlight can play a particular track in your library and look up other artists, tracks, and albums in the iTunes Store, but it can't play an album by name. Butler and LaunchBar can (though not Alfred or Quicksilver).
All the launchers except Butler can perform calculations right in the search field. (In Quicksilver, you must type "=" as your first character to trigger the calculation.) In addition, all except Butler let you use Quick Look to preview a selected item without opening it. And all except Butler and Spotlight can open a document in an app other than the default one for that file type (for instance, opening a Word document in Pages), and let you type keywords to perform a wide variety of system actions — things like hiding the current app, changing your volume, or restarting your Mac.
LaunchBar can add an event or reminder from its search window. (Alfred can, too, with the addition of free third-party workflows.) LaunchBar can also fill in user-defined text snippets (including variables such as date and time) and emoji (by name), switch network locations and user accounts, perform any of dozens of built-in actions (such as compressing files, emptying the Trash, hiding an application, and performing text conversions), and execute Automator workflows and items on the system-wide Services menu. It also lets you perform other actions with selected files besides just opening them — sending files by email or Messages, running an AppleScript, and so on.
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