Mojang AB, the maker of Minecraft, offers a free demo of the game for download on Minecraft.net, as of July 2015. Directly below the orange Get Minecraft button is a small link with the text that reads Play the Demo.
In order to download the demo from Minecraft.net, a user must first register a Mojang account and log into the Minecraft launcher. The demo allows users to play for 100 minutes (or five Minecraft days) before the map locks and the game is reset. Resetting the game also resets the 100 minute timer, which allows a player to use the demo as many times as they wish.
The download is available for both Mac and PC computers.