OpenProj is a free project-management package that substitutes nicely for Microsoft Project but works with Linux and Mac as well as Windows. With more than a million users, OpenProj's installed base is second only to that of Microsoft Project itself--which, of course, costs a heck of a lot more. Gantt charts, PERT charts and all the other capabilities offered by Microsoft's software are in OpenProj as well, and existing Project files can be easily imported.
11. Antivirus: ClamAV
Even if you're running Linux, it's still a good idea to use some kind of antivirus software. Originally designed for Unix, ClamAV is a nice package that's now available for Linux as well as for Windows and a number of other platforms. The tool offers built-in support for almost all mail file formats as well as popular document formats including Microsoft Office, HTML, RTF and PDF. With a virus database that's updated multiple times per day, ClamAV is, of course, also free.