Not specifically software, but I divide my donations into three categories - for my budget, that's basically the $10-20 range, the $20-500 range, and $500-2000. I track the donations I make over the year, with a target in mind. For me, the target is 10% of income.
I decide which organizations are doing the most important work, and prioritize those. I try to donate monthly to those that I make use of regularly, then I give the rest as what comes up from day to day.
I consider free software to be a social good, so I don't separate it from other giving.
Don't worry, deceptive sales are still allowed everywhere else...