I have Microsoft Project. However, it is not available for Mac OS X or Linux. So, a multi-platform Open Source alternative is good to learn about. I just read about...

OpenProj 1.4

It runs on Microsoft Windows as well as Mac OS X and Linux. So, I might be taking a closer look at it in the near future. However, I think it is odd that this so-called Open Source package is only available as a binary download from SourceForge. I also wonder why it does not look like it has had any development activity since September 2008. Dead project?