I subscribe to GiveawayOfTheDay. They offer free software every day that has a licence valid for a year. At the end of the year, you either buy a licence or the programme lapses. However, with cutters, converters and so on, there is a new offer from a different company virtually every 15 to 25 days, so one never needs actually to buy anything, just use the latest download.
It's different with other products. I bought a licence for Zemana antilogger after the giveaway period ran out as it is a fantastic programme. I have paid for some other stuff too at the end of the period. I guess this is how the companies absorb the loss - there will always be some people who will renew for hard cash at the end, even for a converter they have grown attached to and are reluctant to use another. I must say that I can understand that as some of the converters will embed subs and some won't, for instance, or have far more functions.
I hope this is a solution to your query. By the way, the giveaway versions are generally not upgradable, so you have to be careful. If you get a message asking if you want to upgrade to "the latest" version a few months later, do not do so as this will wipe the free licence key.