Bricksmith

Bricksmith lets you create lego models using your mac. There is a large array of parts available and once you get the knack of assembling these in 3D space you can make very realistic looking models. The highlight is probably the Minifigure generator which builds lego people for you - perfect for creating a forum profile image of you which stands out.

Developer's site

Processing

Processing is an open source Java-based development environment that aims to make it fast and easy to program prototype software (each project is known as a "sketch"). While the basic syntax is of a Java nature, many libraries have already been created to make programming using Processing simple and fast.

It supports serial communication, making it a useful tool to work with electronics boards like the Arduino (a versatile opensource project, which can even be used to send data back to your mac to run applescripts using Applescript Proxy)

For budding programmers, this is a great environment to learn, with a large amount of support from their website.

Developer's site

Portable Apps

After a short break, I've decided to get the ball rolling again with a link to an array of standard mac applications which have been made portable, allowing you to keep them on your USB key-ring and run them directly from flash memory on any mac you visit. The list of apps that have been modified to do this is substantial, containing the core mac apps like Mail and iCal as well as other major opensource programs like Gimp, Audacity, Nvu and Openoffice.

Developer's site

PicLens

While not an app, PicLens is a very cool plugin for Firefox 3 or Safari 3.0 (sadly not 3.1 yet). It installs a button next to your google search box that allows you to browse online photos and videos in a 3D environment, making the process of searching Flikr, Google Images, Amazon and Youtube a lot more fun. The graphics are extremely smooth, and you can navigate using mouse scrolling or arrow keys. Double clicking on a photo makes it fullscreen, and there is an option to launch the photo in your browser for downloading.

Developer's site

Tip: To use this on a local folder of photos, drag that folder into your browser window and then start PicLens.

xBench

Okay, so you've bought your shiny new mac, and you want to see how powerful it really is. xBench is a free app that lets you run a series of tests including CPU, RAM speed, graphics and disk read/write speed tests. 

While the graphics may not be the prettiest of benchmarking software, the app lets you upload your stats to a central server and compare with other mac users. This could be useful for checking if that RAM upgrade really is worth the cash.

Developer's site

MacOSaiX

This app probably won't be used by you every day, but it's worth checking out - I install apps like these in a 'playground' folder of apps I don't use very much, but are cool to have. This program is similar to the mosaic screensaver that comes with leopard except, after giving it an image to work from, it fetches other images from the internet (Flikr, Google as well as iPhoto) and places them in the collage according to brightness for you.

Developer's site

Porticus

Porticus is a front-end for macports which makes it easy to install linux applications on your mac. It takes the terminal-based system of installing packages and turns this into a neat Cocoa app which even lets you search and browse ports and modules with description tags as if they were finder items. Ports can easily be activated/deactivated and updated, allowing for easy managment of your linux ports.

Developer's site