Besiege is a physics-based game in development by Spiderling Studios in the United Kingdom for Windows, OS X and Linux. The game was released in early access on Steam on 28 January 2015. The game allows players to build outlandish medieval siege engines to pit against castles or armies. Players select from a collection of mechanical parts that can be connected together to build a machine. Each level has a goal, such as "destroy the windmill" or "kill 100 soldiers". Although the goals are relatively simple, the wide variety of possible approaches allows for experimentation. Despite the medieval theme to the game, players are able to build modern vehicles such as tanks, automobiles, bomber planes, propeller planes, airships, and battleships. An update in December 2017 added a level editor and multiplayer capabilities, such as pitting the vehicle creations against each other, or other players attempting to knock down a castle created by another. Marsh Davies of Rock, Paper, Shotgun praised an early version of the game, comparing its "bouncily caricatured" science to a 12th-century version of Kerbal Space Program. Davies also praised the game's stylized graphics and sound.