Using “Free” Tools for Multi-Project Management \ PMO Hackathon

I went to the recent PMO Flashmob Hackathon. For those of you that aren’t familiar with the concept of a Hackathon, it’s an event where programmers get together to write (or “hack”) some computer code over an extended period (hence “-athon”, from the ending of “marathon”) to solve problems posed by the attendees.
PMO Flashmob decided to hold one of these, with a PMO focus. I was initially somewhat wary. I have done a bit of programming in my time (Fortran, Java and VBA if you’re interested) but most of that is quite a while ago now (I did say some of it was Fortran), and I was concerned at the little I would be able to “bring to the table” for a hackathon. A week or so before the event, a post came out from host John Mcintyre saying the PMO hackathon would have a less technical focus than typical for traditional hackathons, so I took the plunge and signed up.
But we had been asked to come up with a suggestion for something to work on. So what to suggest?
I have seen much discussion heated debate on the web on the merits of Project Portfolio Management (PPM) tools vs. Spreadsheets, including this comment from PMO Flashmobber Nicole Reilly “Part of my initial discussions with a potential client will be to assess their openness to using […] the ever-increasing number low-cost or even free tools now out there”. This prompted me to wonder:
What useful PPM functionality can be implemented using just free (or nearly free) tools?