I did some more research for other solutions, but the results are not plenty. I have little experience with massive multiplayer development and it's requirements, so I just listed everything I found worthy showing. (Yes, 3 results and 33% plausible for usage ).


Some products I think are not up for the task:

http://opensource.linuxgamepublishing.com/grapple.php
Although it sounds better than 3dgs's current functionality, it's somewhat too basic. (the readme has more specific descriptions).

http://enet.bespin.org/
Well, it's actualy already saying so on the main page.


One hidden gem that may be up for it:

http://jcatki.no-ip.org:8080/SDL_net/
http://www.libsdl.org/
SDL_Net I got recommended by a MMORPG developper that wrote an interesting article about MMOG's on devmaster. This solution is not as big as raknet either, but it's clearly capable of handling a mmorpg.

Article: http://www.devmaster.net/articles/building-mmorpg/
Note that he also recommends Directplay, this either means some people here are wrong, or he is wrong. But he proved his point already by succesfully creating a mmorpg. Although not with dplay, I expect from him to know what he is talking about.

Game in dev: http://www.eternal-lands.com/
Players online: http://game.eternal-lands.com/online_players.htm
That made me quite exciting indeed, and the article was a good read.
Another note: There is a big community for SDL (as well on IRC), which is a big plus for me ^^.

It doesn't look as professional as Ragnet, but I think it could be a good alternative, especially for beginners as there is alot of support and tutorials.