Hopf Topology Archive, Revised Version Science, Math, Publications, Subject Preprint Archives - Hopf Topology Archive. Algebraic topology and related areas. https://hopf.math.purdue.edu/
Optimization Online Science, Math, Publications, Subject Preprint Archives - Optimization Online. A repository of eprints about optimisation and related topics. https://www.optimization-online.org/
Shelah's Archive Science, Math, Publications, Subject Preprint Archives - Shelah's Archive. Papers by Saharon Shelah in logic and related. https://shelah.logic.at/