Added a lifetime tier across all apps this month, alongside the monthly and yearly options. The people who'd been using my apps for a while and still hadn't subscribed were never going to start a recurring payment, so I wanted to see if a one-time commitment was a different question for them.
Revenue went from $18 up to $25/mo, the biggest jump since I started the series. One of those is a lifetime sale, the first since I added the tier.