It's a brand-new (and very, very rough) Mac OS X text editor that wraps a slick GUI similar to the semi-abandoned Espresso around an editing engine with support for TextMate bundles and — this is the crazy part — Vim's editing modes and key bindings.
So far the word to describe Vico is incomplete. It support a lot of the core Vim feature set, but lacks keyboard shortcuts for switching between tabs or splits. It has project and symbol browsers, but those UI panes mysteriously lack inset padding. And I'm concerned that while there's sometimes nothing more powerful than one developer scratching an itch, building a text editor robust enough for programmers' day to day use is a tough job, and this Martin guy won't see it through — we've been burned before.
But this is a promising project, worth keeping an eye on. Even if it doesn't turn out to be a successor to TextMate or BBEdit it could be a really interesting app.