As things stand right now, I don't want to spend either money or a lot of time on this. I've managed to move most of my flows over to a combination of native SmartThings automations (for simple rules that don't need any constraints), SmartRules (an iOS app that includes only if type constraints), the native Hue app, IFTTT, WebCore, and Alexa. Most of it is working, although I'm still doing a lot of troubleshooting.
It's certainly not as elegant a solution as Stringify was.
Most of my lights are Hue. SmartThings has no exposure to Hue groups and scenes. I have 5 lights in the kitchen and use three motion sensors to trigger them. If I use SmartThings to turn them off and on, it does so one light at a time (aka the "popcorn" effect). I could buy Hue motion sensors and change it over to Hue, but there's limitations on time of day, there, that won't work the way I want it to. So I'm using SmartThings to check for motion, and IFTTT to do the actual on during the day. But IFTTT lags. There's just not a good solution for my use case, there. Hue work great for slowly and smoothly changing my lights over to a warmer temperature at sunset, though.
I resorted to WebCore for flows that have timers, because that seemed the easiest way to do that. We'll see how that works out.