DragThing is shareware: You can download and try it for free, and if you decide to keep it pay $29. The current version of DragThing supports Mac OS X Tiger or later, but earlier versions are also available for earlier versions of Mac OS.
Quicksilver is a free Finder alternative for OS X Tiger and newer Mac OS versions; it lets you launch applications and locate specific files quickly just by typing the first few letters of an application or file name. It's a simple, keyboard-centric way to launch apps and open files. Like Alfred, it learns your preferences and orders results accordingly, and it lets you assign keyboard shortcuts to a wide variety of actions.
Mission Control looks like it will be an interesting combination of existing Mac OS X features -- full-screen apps, Spaces (Apple's virtual desktop feature), Exposé (which allows you to see thumbnails of all Spaces, open windows and items hidden by windows, and to switch apps) and Dashboard (a feature that allows easy viewing of a range of widgets, or tiny applets) -- in a single interface.
In bringing these elements together, Apple is attempting to offer a one-click view of all running apps, windows, full-screen app views and Spaces. The ability to swipe through all these items will borrow from the iOS ability to swipe across multiple home screens.
In the new iteration, Dashboard appears to have its own Space or full-screen view instead of appearing as an overlay to the desktop as it does currently. While I'm not enamored of that particular change, overall I think the Mission Control concept is solid as a way to quickly see everything that's running on a Mac and to easily switch to the tasks you need.
I'm not aware of any existing tools that match the complete integration of these features that Apple is promising in Lion, but here are three that offer useful enhancements to Spaces and Exposé along the lines Apple seems to be planning -- and which may even be better than Apple's ultimate Mission Control solution for some users.
Hyperspaces extends and customizes Apple's implementation of Spaces. It lets you assign custom desktop pictures to each Space for easy recognition (or just tint the desktop picture of each space a different color) and name/label each Space -- useful if you routinely dedicate different Spaces to different tasks.
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