Airfoil is just one of a list of fantastic audio apps from indie developers Rogue Amoeba.

Does your Mac’s desktop look like this? Or like this? If so, you need help. More to the point, you need Clean.

Bean is one of OS X’s little treasures. It’s a lightweight rich text editor that’s nimble, fast and offers just a teeny tiny bit more than Apple’s own TextEdit. And does all this for free.

Structurer is a clever free tool for rapidly creating file and folder trees without any messing about in Finder.

Onyx is a free system maintenance tool for Mac OS X.

One of the nice things about Onyx is that it covers everything you can think of. It’s packed with tools that you might want to use often, plus some you might use only once in a blue moon. But they’re all there, in one place.

If you spend a lot of time using a lot of webapps, Fluid should be high on your list of software must-haves.

It’s been hovering in unofficial beta status for years now, but just this week got bumped to 1.0, and now comes in two flavors: free and paid. Either of them is well worth having.

MarsEdit is the best blogging tool for OS X, bar none. If you do blogging for money or just for the love of it, MarsEdit is a dream come true for you. It will save you lots of hassle and hours of time.

If you’ve ever used and loved the “Archive” function in Gmail or MobileMe, then found yourself missing it while using Apple’s own Mail application, this simple free plugin is a dream come true.

It’s an Archive button for Mail, and you can guess what it does. Instead of having to mess around with filing messages into folders, a single click will throw them into the archive. It even comes with its own ready-made keyboard shortcut (Command+Option+S), to make archiving even faster and easier.

When you need to find something specific, use Mail’s own search, which is quite up to the task of hunting through enormous archives (I’ve used Mail in this way, as a backup for my Gmail account, for years now).

If you need Mail to be a little more flexible, try Mail Act-On, which we mentioned back in number 8 in this series.

(You’re reading the 33rd post in our series, 50 Essential Mac Applications: a list of the great Mac apps the team at Cult of Mac value most. Read more, or grab the RSS feed.)

Applejack is a command-line application for rescuing your computer when disaster strikes, or threatens to strike.

Don’t let the “command-line” bit frighten you off. Applejack is probably the easiest-to-use command-line application I’ve ever seen. It was built for ordinary people to use, and won’t bamboozle you with geekspeak.

YoruFukurou (“Night Owl”) is a high quality, totally free Twitter client that will appeal to a wide cross-section of people.