There are two *online, evolving, collaborative "foundational text" projects for research mathematicians* that I am aware of:

(1) [The Stacks Project][1] for algebraic geometry

(2) [Kerodon][2] for categorical homotopy theory

I find them admirable, valuable and suited to our times - sort of Bourbaki for the internet age. I'd like to know if there are others of the *same nature* that are ongoing or in the offing. 


  [1]: https://stacks.math.columbia.edu
  [2]: https://kerodon.net/about