We have several web applications that we wish to present under one single page application. We are looking for a micro-frontend architecture/framework to use. As we see it,
This topic is pretty old, but still, maybe someone will find it interesting to read the answer later because it's still a very good topic.
This package you've posted in your question - https://github.com/single-spa/single-spa looks very good and we tried to work with it, however, it has too many framework-specific things, that makes onboarding for new engineers super difficult.
I think first you need to choose the approach for the microfrontend composition of your application:
I've tried to describe them with some useful links in the article https://medium.com/@danielostapenko/frontend-architecture-in-scale-for-large-organizations-593930ed10cd
Also, I would really encourage you to look at the Module Federation feature provided by Webpack 5. It looks super promising and comfortable to work within the micro-frontends world.