Cube is a Magic: The Gathering limited format where all the cards come from a pre-prepared pool of cards that were chosen for the purpose of playing limited with them. The format originated in Toronto, Canada and spread from there. I found out about the idea from Gabe Walls, and about a year later I started building my own. Consider this a guide to the cube experience, both for cube caretakers and players.
A cube is a large pool of cards selected for the purposes of limited. It should should contain at least 360 cards so that you can support a standard eight-player booster draft. The actual selection of the cards will depend on the feel that you want games of your cube to have. Ben Bleiweiss owns a box containing one copy of each unique card that has been printed that he uses to draft, and although he does not call it a cube, it could be called one. On the other hand, my cube contains 410 cards, and almost every card is strong enough to have seen constructed play at one point or another. However, I have tried to avoid cards that make games unfun by being too powerful, such as Black Lotus, Wheel of Fortune, and Ancestral Recall; Gabe Walls does not worry about this, and includes pretty much anything and everything in his cube.
What you put in your own cube will reflect what you want out of it. If you want to have really powerful games, you can build something similar to mine. If you just want a change of pace but prefer limited to constructed, why not make a cube with all strong limited commons? Even a cube consisting of cards from only one block could be interesting. Your imagination is the limit.
Practically speaking, the cube should be sleeved so that expensive cards don't get destroyed. You will also need to have enough sleeved basic lands to go around.
In general, the cube is drafted. Eight-player team booster draft is my preferred format, because having eight players makes it feel most like a normal draft and using teams means that no one has to lose and not play anymore. However, any limited format can be played with the cube. I have killed many between-round breaks by playing cube sealed, and I have also done an eight-player Rotisserie draft- that is, we put the entire cube face up on the table and rochester drafted the entire cube all at once. This was riotous fun and attracted many confused spectators. To do a normal booster draft, have everyone shuffle the cube together and then make random fifteen card packs out of the randomized cards. Then, draft, add basic lands, and play.
A cube must be constructed very carefully. In general, it is important that a cube have equal numbers of cards in each color, enough creatures in each color for everyone, and a mana curve within each color. It is also important that the each color have a similar power level. Past that, do what you think is fun. Balancing the cube in power level is much easier when you make consistent choices across colors. You wouldn't want to put a bunch of strong limited cards in white and then fill red up with the best burn that has ever been printed. My cube began with only cards that were legal in legacy or unrestricted in vintage, but a few cards that I deem to be fun and not overpowered are now allowed to break that rule. You also want to be able to accomodate eight players, which means having at least 360 cards. I used to have exactly 360 cards because I liked having every card in play when we did an eight-player draft. Adam Prosak's cube has something like 400 cards, as in Arizona they prefer to not have every card available every time; I now subscribe to this philosophy, since it leads to more variety and interest.
The way I originally balanced the colors when I built the cube was to lay out each color in the same way that one lays out a limited deck and make sure that things were reasonable with respect to mana curve and creatures. Most of the implications of the cube design decisions you make will not become clear to you until you have drafted your cube multiple times, so don't worry too much about getting it right to begin with and just try what you think is reasonable. Eventually, you will figure out what your preferences are and adjust your cube accordingly.
The following is a random fifteen card pack you might "open" while drafting my cube:
Umezawa's Jitte, Carnophage, Psychatog, Living Death, Serendib Efreet, Ravenous Baloth, Grim Lavamancer, Flooded Strand, Fireball, Isamaru Hound of Konda, Rofellos Llanowar Emissary, Gaea's Cradle, Capsize, Decree of Justice, Lightning Helix. Choose wisely.
This is my deck from an actual draft:
Isamaru, Hound of Konda | Mother of Runes | Savannah Lions | Jackal Pup | Mogg Fanatic | Grim Lavamancer
I went 3-0, 6-0 with that deck. In the first round, I beat someone who was playing Recurring Nightmare-Survival of the Fittest green-black. He also had not drafted green acceleration highly enough, so I was able to run him over quickly with the highlight of the games being when I Demonfired his Genesis. In the second round, I played agianst the other player who was taking red burn spells, but he had paired it with black. My Paladin en-Vec took down game one, and I managed to outrace his Cursed Scroll in game two with Lightning Helix. In game three, I played against a blue-white control deck. I thought I had game one in the bag when I cast Ravages of War on turn five, but he played Teferi in response, so I had to sneak my creatures in with Mother of Runes instead of just killing him in two turns. In the second game, he tapped out for Winds of Rath with Treachery backup for my next threat, but that next threat was a Calciderm and it went all the way.
If that doesn't make you smile, then I have no idea why you're reading this page. Cube is the most fun I have ever had while playing Magic. I have played at kitchen tables, in grade school classrooms, at local stores, at gaming conventions, and on the pro tour, and no Magic that I have ever played holds a candle to how much fun drafting a well-constructed cube is. After all, we are all playing Magic for fun, right?
The actual list of my cube is here. My cube is almost excusively either legal in legacy or unrestricted in vintage, with a few exceptions. Almost everything in my cube has been significant to constructed at some point in Magic history. This means that the cards in my cube are very powerful, and games feel more like constructed than limited. I enjoy this power level, although it is too high for some tastes. To each his own. Two more cubes are listed on this site; the links to those lists are at the top.
The majority of the cards in my cube are foreign. I really enjoy foreign cards, and I spent about a year as a very active dealer, so acquiring interesting cards for the cube became a fun challenge for me. It now frightens me just how far I have gone, but I am trying to go further. If you play my cube, enjoy it, and are feeling generous, I will happily replace your foreign card with my English one. These substitutions are very much appreciated.
Brett's cube. Brett appears to be originally from Canada, and he keeps this updated resonably often.
The Cube 2.0, by Evan Erwin. This cube is located in Texas.
Gleaning the Cube, by Sam Gomersall. This is Sam's personal cube, although it is a very outdated article.
Fun^3, by Noah Weil. This is a report from a draft of the Toronto cube.
All of the following people have contributed cards to my cube: Sam Stoddard, JR Wade, Erik Klug, Jake Meiser, Justin George, Saran Aiyappasamy, Adam Yurchick, Ben Wienburg, Max Young, Nether, Matt Westfall, Ervin Tormos, Mike Belfatto, Matt Westfall, Matt Gunn, Aaron Cutler. Thanks to all of those for their generosity.