Moonstone: A Hard Days Knight, is a video game developed and published by Mindscape in 1991. It was released on the Amiga and one year later converted to MS-DOS with alternate sound and music. The title is a play on A Hard Day's Night. Moonstone's gameplay blends several different genres, including strategy, real time fighting and role-playing video games. It allows up to four players to participate in a basic turn based Role Playing Game with real time combat for any encounters. It is also notable as one of the goriest games of its time, with some exceptionally bloody fight and death scenes.

The player takes on the role of a chosen knight who is sent by the druids to return the mystical 'moonstone' to Stonehenge. The game supports between 1 to 4 players at once, with the computer controlling any knights not controlled by human players as rival NPCs.

The world map is divided into 4 distinct regions:

Misty Moors: The NW region of the Blue Knight (Sir Godber). Monsters found there are the Axe and Spear-bearing Troggs as well as their War Beasts. There is also the city of Highwood with the High Temple where the player can buy and sell magical items.

Wetlands: The SE region of the Red Knight (Sir Edward). Monsters are the Trolls and the Mudmen. There is also the city of Waterdeep with Mythral the Mystic who can advance the player's abilities in exchange of gold (or randomly reduce them).

Great Forest: The SW region of the Green Knight (Sir Jeffrey). Monsters are the Troggs and the Ratmen. It features the Stonehenge where the player can gain a life by donating a magical item.

Northern Wastelands: The NE region of the Orange Knight (Sir Richard). Monsters include Troggs and Baloks. It also features the Tower of Math the Wizard who can randomly reward the player or transform him into a frog if he asks repeatedly.