Downloading DrDJ 3.1 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The software lies within Audio & Video Tools, more precisely Players. This free Mac application was originally developed by e dot studios. We recommend checking the downloaded files with any free antivirus.
From the developer:
DrDJ is a little applications for DJ Wannabe's. It can play MP3s, AACs (and any audio file CoreAudio can play) and allows you to fade between songs. You're in controll of the transition, but DrDJ can do everything automagically too.The on-the-fly playlist can contain an infinite (okay, so it's limited by the size of your computer's memory) number of songs, so you can fill it, let DrDJ handle everything and go enjoy your party!
You may want to check out more software for Mac, such as Amarra Mini, MacAppStuff Sounds or HALion Player, which might be similar to DrDJ.