Forrest Cameranesi here, lead designer of Eternal.
The last version of Eternal publicly released was still in a very "1.0" state, and I'm not incredibly proud of that. There's a lot more polish that could be done to it, and numerous other prominent figures in the Marathon development community, such as Crater Creator of Excalibur: Morgana's Revenge and RyokoTK of Phoenix, have written extensive reviews outlining some of these points, which I planned to use as to-do lists for future revisions (see their reviews here and here).
Beyond that, a number of things were cut to get a playable 1.0 out the door, and these were planned to be incorporated into a truly final version to be called "Eternal X Omega". Among those cut features were new high-res renders of all the weapons, players, and Bobs, a handful of multiplayer maps (at least one in each environment), and a five-level cooperative "Vidmaster's Challenge" of sorts.
Along the way, some changes to the middle of the story occurred, and a couple levels got shuffled around or replaced in the process. Because of this, I planned to release a version 1.1 incorporating those changes and the other improvements thus far prior to completing Omega. But even that took over seven years to get out, as real life sapped any semblance of time or energy to keep working on this project from me. And I've since moved to a newer computer and don't even have access to the old familiar toolchain I used to develop with.
But I feel bad letting this project languish, especially as I see people are still downloading, playing, and talking about it to this day. So I'm calling for help from any fans of this project with skills and time to lend, to maybe help carry it over the threshold into something a little more polished. I don't have high hopes or aspirations for implementing new multiplayer or cooperative levels, but I have a full set of mostly completed Cinema4D weapon models awaiting rendering, plus all the minor tweaks and improvements suggested in the reviews above.
So if you'd like to help this project really shine, drop me a line at firstname.lastname@example.org and lets see if we can't set something up.
The Eternal Maps merge folder is also available for public development on GitHub. Anyone who would like to contribute by editing the map file may do so at your leisure that way, and your contributions will be rolled in to the next public release of Eternal.