If you are a nonprofit professional who keeps hearing about open source software and doesn't know how to begin thinking about it, it's nice to know that the folks at the Nonprofit Open Source Initiative understand your feelings and your needs.

NOSI (as it is also known) has come out with a primer on open source software for nonprofits, and it is a very good one indeed.

You can read it online, or download a printable version.  I especially recommend the case studies and the appendix of frequently asked questions (and their answers).

Here are some examples:
I don't see open source software as a magic solution for every technical challenge that a nonprofit or philanthropic organization faces, but it presents you with a range of strong options.  And since knowledge can be power, I recommend that you know your options.