Modified Newtonian Dynamics (MOND), kicked off by Moti Milgrom in 1983*, is the subject of an impressive number of papers.

Its track record wrt the rotation curves of spiral galaxies is particularly impressive.

However, right from the get-go, MOND was seen as having some serious short-comings, both theoretical (e.g. it is incompatible with relativity) and observational (e.g. cluster motions).

Several attempts were made to extend MOND, to address the theoretical short-comings. Perhaps the most well-known extension (if it can be called that) is Bekenstein's TeVeS, see here for a primer.

While I am not a fan of MOND, or TeVeS, if anyone would like to ask about the extent to which either of these match good, relevant astronomical observations, I'd be happy to try to answer.

* Milgrom, 1983