This list misses "Everything", the instant file search engine. It's the app I miss the most on Linux and OS X. (http://www.voidtools.com/)
Everything's secret is that it taps into the file system journal to instantly know about any file name change. On *nix systems "locate" needs to manually rescan the whole HD to update its database, so you can't use it to quickly find a recent file, and Spotlight on OS X is just a joke when it comes to finding a file by its name. (Or when you simply want to know where a file is)
"VoidTools Everything Search Engine - Sometimes you just want a text box, a 300k application and you want to Search Everything. This tiny utility makes it super easy to search your entire hard drive (all of them actually) instantly. You can Google the whole internet with Bing in a second, why shouldn't you be able to do the same with your hard drive. Best part is that it works on any version of Windows, even Windows 2000."
Everything's secret is that it taps into the file system journal to instantly know about any file name change. On *nix systems "locate" needs to manually rescan the whole HD to update its database, so you can't use it to quickly find a recent file, and Spotlight on OS X is just a joke when it comes to finding a file by its name. (Or when you simply want to know where a file is)