We built the website on Squarespace ( a tiny bit of custom JS because I wanted a specific UX, but minor). When we are fully launched and selling product, we'll probably continue to use squarespace, but we'll see. It suits us for marketing purposes and capturing interest now.
At the same time, we're working in the hardware space (healthtech building an EEG), so we write all of our firmware, and we've got AI running on google cloud, so all the data pipelines that go along with that.
We're building the front-end for our mobile app, but using Google Firebase for the user account, and other simple user-data stuff that we need. I consider Firebase to be mostly no-code, I code up the front-end, but don't need to do anything on the backend.
The more interesting thing I've heard of recently is Fl{0} (https://fl0.com). They're a Sydney based start-up that is building a low-code style backend system. I'm not completely sure I get it, maybe it's just another version of nodeRed, and other similar tools.