Clonk is a single player and multiplayer computer game series. The games feature a mix of the action, real-time strategy and platform game genres. Developed between 1994 and 2014 by RedWolf Design the games of the series were originally released as Shareware and became around 2008/2014 Freeware and open source software. The game's community develops since then the series under the name OpenClonk. The game series was compared and described as mixture of Worms, The Settlers, Tetris, Lemmings and Minecraft. The game was noted for the easy game "extension" mechanic with an integrated editor and developer mode, which allows experienced players to create their own modifications directly into the game.
Source: Wikipedia, "Clonk", available under the CC-BY-SA License.