Freeware

The Battle for Wesnoth
Entertainment, Games, Video Games, Strategy, Freeware - The Battle for Wesnoth. A turn-based game with a fantasy theme.
http://www.wesnoth.org/
Crimson Fields
Entertainment, Games, Video Games, Strategy, Freeware - Crimson Fields. Describes tactical war game for Linux or FreeBSD in the tradition of Battle Isle.
https://crimson.seul.org/
UFO 2000
Entertainment, Games, Video Games, Strategy, Freeware - UFO 2000. A multiplayer remake of X-COM: UFO Defense for Windows.
https://ufo2000.sourceforge.net/
L-O-C Homepage
Entertainment, Games, Video Games, Strategy, Freeware - L-O-C. Turn-based strategy game with some strong RPG elements, based on a game by Julian Gollop.
https://l-o-c.sourceforge.net/
Freerails
Entertainment, Games, Video Games, Strategy, Freeware - FreeRails. Multiplayer real-time strategy game inspired by Railroad Tycoon and Railroad Tycoon II.
https://freerails.sourceforge.net/
CivQuest - Welcome!
Entertainment, Games, Video Games, Strategy, Freeware - CivQuest. Turn-based Civilization clone written in Java.
https://civquest.sourceforge.net/