http://store.steampowered.com/app/70/ is available for Mac/Linux now. You can install the Linux server binary, but it won't start from the Steam GUI.
Image may be NSFW.
Clik here to view.
If you try to do so via the command-line it backfalls to Half-Life 1 (player models are barneys, VGUI is broken, ...) because the cl_dlls is Windows-only.
Image may be NSFW.
Clik here to view.
As a huge fan I offer my help to port Natural-Selection 1. Can you publish the source code of the client library?
Image may be NSFW.
Clik here to view.

If you try to do so via the command-line it backfalls to Half-Life 1 (player models are barneys, VGUI is broken, ...) because the cl_dlls is Windows-only.
Image may be NSFW.
Clik here to view.

As a huge fan I offer my help to port Natural-Selection 1. Can you publish the source code of the client library?