[aaronem]

Lusty actually originated on the Vim side, and was ported to Emacs by someone who liked the functionality.

Emacs comes stock with good tags support; once you've built a tagfile, M-. on a tag will take you to its definition. (I don't use tags myself, although I really should, so I don't know whether Emacs can automate construction and update of a tagfile, but I strongly suspect it can; check the relevant documentation for details.)