TodoMVC is a very well known (like ~27K GitHub stars known) application among developers as it is a really great way to start to learn a new Model-View-Something framework. It has plenty of samples done with different frameworks, all implementing exactly the same solution. This way is very easy to compare them against each other and see what is the one you prefer. Creating a To-Do App is easy enough, but not too easy, to be the perfect playground to learn a new technology.
The only issue with TodoMVC project is that it « only » focus on front-end solutions.