Forge

Forge is a free, open source implementation of the Magic: The Gathering ruleset, written in Java.

Cards from every expansion ever released can be used in games for up to eight players, against either computer opponents, or other human players on a local network or over the internet.

Included are several puzzles, where players can attempt to solve M:TG-related puzzles and tracking thereof.

It also comes with a Quest or Adventure Mode that reimagines the "Shandalar" setting of Magic: The Gathering where the player explores the plane of Shandalar and battles foes in magical battles along the way, earning gold and new cards.