CLPMR provides the same functionalities as procmail but with much more flexibility and simplicity due to the fact that the language you describe the rules with is Lisp and not some obscure sequence of characters looking like line noise. Using Lisp, it means that the implementation of things like mailing list servers and document servers becomes trivial and you don't even need external programs (see this example). MIME content is handled natively as well.
Homepage: http://wcp.sdf-eu.org/software/#clpmr
Download: http://wcp.sdf-eu.org/software/clpmr-20150207T212625.tbz
License: GPL