Software with the LIGHTEST foot print?

A recent conversation thread about SeNuke started me wondering about this. Sure, there's a lot of software out there that's brutally efficient... but they also seem to be about as subtle and delicate as a hammer. Which might be very good for certain people, but what about those who value foot print over volume?

What are the lightest softwares then? And how possible is it for a software to even be light... or is a messy foot print a result of design?

Hmm....