IELR(1) a niche LR(1) parser generator. More well-known are LALR and Pager’s “minimal” LR(1) algorithm (PGM(1)), but IELR(1) can generate a parser for certain grammars that those cannot. This post by the same authors goes into more detail about the problem IELR(1) solves.

The linked post is about implementing IELR(1), in particular the challenges the authors faced doing so.

They’ve implemented IERL(1) in their own parser generator, hocc, that they’re writing for their own language, Hemlock: “a systems programming language that emphasizes reliable high performance parallel computation” that is (or at least very similar to) an ML dialect.