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

(1) The Stacks Project for algebraic geometry

(2) Kerodon 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.