The 2.1.3.15 version of Dominion for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program lies within Games, more precisely Card. This free Mac app is an intellectual property of Making Fun, Inc. We recommend checking the downloaded files with any free antivirus.
From the developer:
Dominion is the original deck-building card game that has won numerous awards and spawned an entire genre. Build up a powerful kingdom of knights, nobles and witches to conquer duchies and provinces. This connecting game client enables you to join the global community of Dominion players, as you compete online against 1-5 other real players or against AI bots in campaign or practice games.
You may want to check out more Mac applications, such as LostInReefs, which might be related to Dominion.