Pianochords [is a Dashboard widget which] shows and plays all the musical chords you can think of. Just press a key on the keyboard to set the root of the chord and click the display to select the derived chord. It’s as simple as that!

Pros: Pianochords is an excellent tool for those of you who are studying and/or practicing music theory, music composition, or general music.

Cons: None significant.

Ubuntu offers you a complete Linux-based operating system, including all the major applications you need to play and work. With a strong focus on a desktop that “Just Works”, Ubuntu is a great choice for home or the office. The base system and all included software is free, and support is available from the community or by professional support providers.

Pros: Ubuntu is a powerful and free operating system. The default installation process is incredibly user-friendly and includes almost every application that you would ever need to get started in the world of Linux, an easy-to-use installer for additional applications, and an easy-to-use software update engine. Ubuntu is a cross-platform operating system for PowerPC Macs, Intel x86 PCs, and AMD64 PCs.

Cons: Ubuntu does not support AirPort Extreme cards at this time. The blame for this lies entirely with Broadcom, as they have refused to provide native Linux drivers and specifications for the chipset that powers the AirPort Extreme cards.

Pac the Man X is a clone of the arcade classic Pac-Man, but it has much better graphics, gameplay, and sound effects. And, it has a level editor! With its simple interface and ease of use, you can create new levels in no time.

Pros: Pac the Man X is the best Pac-Man clone available for Mac OS X.

Cons: None significant.