This section lists middlewares that were somewhat prominent in the past, but were replaced by alternatives down the road.
nrepl-middleware, part of ritz that provides a variety of nREPL middleware supporting various enhanced REPL operations (including apropos, javadoc lookup, code completion, and an alternative eval implementation). (superseded by cider-nrepl)
Javert provides a basic object inspector. (superseded by cider-nrepl)
nrepl-profile: profiling middleware, which was eventually integrated into cider-nrepl.
This list doesn’t aim to be complete. You can find more 3rd-party middlewares listed here.