NetHack - A Free and Open-Source Software
NetHack is a roguelike video game that uses a strategy system. The aim of the game is to ascend to immortality by recovering the Amulet of Yendor from a boss. The game is a challenge that can take decades to beat. To avoid dying in the game, you must use tactics to hoard your resources.
NetHack is available for Windows PCs and Mac laptops. It is free and open-source software. It is released under the NetHack General Public License (NGPL), which is similar to the GNU General Public License. It is also available for Android OS. The graphics are good enough to make the game addictive.
Aside from the standard leveling, the game also has other challenges for players. Players can try to achieve unofficial conducts, such as a vegetarian diet and not killing monsters. These can be tracked by the game and are displayed at ascension and death. There is a community that has developed rules about these things, but they are not officially official.
The game can be difficult and long. As a beginner, you'll probably die a lot. However, you'll quickly learn that you need to focus on something higher than your survival. Once you stop worrying about XP and start worrying about the optimality, efficiency and elegance of your strategies, you'll find yourself immersed in the game.