Benedikt Terhechte (from XING and the Contravariance podcast) has a similar project called AwfulUI[1] to bring some SwiftUI goodness on previous iOS releases. I don't think it's open source at the moment though.
Thanks for mentioning it! There's a plan of open sourcing it. It has different aims than OpenSwiftUI. It is just a back port so that SwiftUI-Like code can be used with iOS < 13. I hope to open source it very soon.