The Battle For Wesnoth:

This is a strategy game that takes place in a fantasy world, where you build armies and launch campaigns against other factions. Graphics are basic but game-play has a good deal of depth to it.

• The Battle  For Wesnoth Web Site
  
  

Battleships Forever:

In Battleships Forever, you control a growing fleet of ships in real time, in an attempt to gain a tactical advantage over your opponent. Graphics are 2d vector-style. Game play is focused on positioning ships strategically for the best effect.

• Battleships Forever Web Site

C-evo:

This game deals with the evolution of humanity from the construction of the wheel up to space travel.You take turns either against the computer or other players (no network gameplay though).

• C-evo Site

FlOw:

Created as a part of a grad student's thesis research, this underwater adventure can be played online or downloaded as a stand-alone version.

• FlOw Flash Game Page

Fracas:

This is an old but still played strategy game based on the goal of world conquest. You can play against the computer or up to 6 other players.

• Fracas Game Page

Gate 88:

Gate 88 is a strategy game based on space combat. It can be played single player or multiplayer, although there have been some recent issues with the multiplayer capabilities.

• Gate 88 Download Page

Spring:

Spring is a game development environment which can be described as a 3d version of Total Annihilation. It is designed for online multiplayer use.

• Spring Project Web Site

Star Wars Tactics:

This is a recently released online strategy board game.

• Star Wars Tactics Site

Steel Panthers:

This is an entire series of tactical wargames featuring both World War II and modern play modes.You can play against a computer opponent, online with others, or even via email.

• Steel Panthers Site