Battle for Wesnoth

Battle for Wesnoth is a turn-based strategy game. I'm not very familiar with role-based strategy games, at first glance it looks like "Heroes of Might and Magic" for me. In this game you are acting in a land called Wesnoth. You have a hero who has to fight against the enemy, for that he can build up (or has already) his own little army. This needs money, to get money you have to conquer villages. Different units (soldiers in your army) have different abilities and weaknesses, the player needs to consider more or less carefully, which units to produce and which units to use in a battle.
The goal of the game may vary in campaigns, but usually player have to destroy the enemies' leader(s) and the player's own hero must survive and/or reach to some point on the map. In general this is up to the developer- it is possible to set any sort of event as the winning (or losing) condition. Usually the length of play is limited by the maximum number of turns. It is possible to define different difficulties of play, for example developer can specify that at "easy" level you get 40 turns and can create 5 types of soldiers, but at "medium" level you have, let's say, 35 turns and 3 types of soldiers available.
Also it is possible to play online against other players.
I have to admit this game isn't too addictive for me, but I'm not a big gamer anyway. For me the most attractive and interesting property of the game is the possibility to create your own campaigns with any goal and tactics you want to or can implement, create your own items and characters with a unique look and behaviour. Due to this an active community of users has formed who are developing the game and missions (forum).