Curse of War is a fast-paced action strategy game for Linux implemented using C and ncurses. Since version 1.2.0, there is also an SDL version.
Unlike most RTS, you are not controlling units, but focus on high-level strategic planning: Building infrastructure, securing resources, and moving your armies. The core game mechanics turns out to be quite close to WWI-WWII type of warfare, however, there is no explicit reference to any historical period.
Multiplayer mode is available.
Packages for popular Linux distributions: