nvi - bug-for-bug "libre" reimplementation of vi
Johannes Zellner's vim pages notably including vimclient
A version of vi that has introduced the notions of displayable buffers, major/minor modes, provides direct X support, ...
VIgor (pronouced like "Igor", Dr. Frankenstein's assistant), the popular Unix editor vi with the addition of the Vigor Assistant, which is shaped remarkably similarly to a dancing paperclip.
This server provides tags file operations to vi-style editors. The server loads and caches the tags data. It may hold multiple sets of tags data for different projects. Each instance of an editor queries the server when a tag is to be looked up. The tags files can be saved gzipped on disk and they will be read directly by the server. The server will do a little compression in memory. By only having one copy of the tags data in memory for all editting sessions a lot of memory is saved and the editor is faster.