There are at least five different promos going on for various Mac shareware right now. If you're part of the Mac fold, I'd say you pretty much "gotta" check out the first two; the other three are cool, but less so.

This is part of what, in my opinion, sets the Mac experience apart from that of other platforms: there is a vibrant ecosystem of independent, small-scale development shops producing stunningly-good apps for free, or for low cost. (Although there's clearly lots of independent development going on for other platforms, there seems to be a much greater variability in the quality.) Promotion events like these give good advertising for those smaller development shops, and give Mac users the chance to try and use good software that they might never have even heard of before. I really think it's a win-win.

I've listed them below, ordered by descending perceived awesomeness.

1. MacHeist - In its second year, you act as a "spy" and solve mission-related puzzles about once a week. Free apps await after you complete each mission, as well as incremental discounts on a large bundle that will go on sale at the end. This is terrifically fun; I can't recommend it highly enough.

I've got a reasonably interesting setup of MisterHouse (a nifty Perl-based home automation program) running on a Linux machine upstairs, that does stuff like turn on lights automatically when it's getting dark or when I enter a room, turn lights off when there hasn't been any activity in a room after a predefined time, and so forth. Maybe I'll post more on that later.