Tadabase, which has been in beta now for some time, has been officially 'launched' today. You can build really nice looking apps with it using a very flexible screen designer:
Very similar to Knack in many ways (check out this comparison https://tadabase.io/tadabase-vs-knack ), it has loads of features for building sophisticated solutions.
More to follow in the next few days in the form of a review and I will add it to my side by side comparison document as well.