Cube is a draft format using a “custom” set curated by our TO, Marshall, and is a “phantom” draft. That is, you don’t keep what you draft — the upside is that the draft is inexpensive to join and you can practice making choices based off the playability rather than the monetary value of the cards!
Marshall’s cube is a Commander cube with a strong incentive to go multicolor (including house-ruling Partner onto all monocolor legendary creatures). It’s a ton of fun, with enough power to let you do nutty stuff, but not so powered that it won’t be accessible to newer players.