Cube is a sealed format for Magic the Gathering, where the creator of the cube will make a curated list of cards to put into these customised packs. Often this is made to be in a singleton format where there is only one copy of any card contained in the cube; this is not a rule however and some of the most interesting cubes specifically play around unique circumstances or builds that have a focal point. One of the most known of which is the Ornithopter Cube which has the only monster in the format being Ornithopters.
For a more thorough explanation than I can give, check out Lucky Paper's explanation and if you're interested 3/3 Elk's Video on the subject.
Why do I enjoy it?Sealed is my favourite way to play Magic the Gathering, I enjoy the deck building aspect as much if not more than the playing aspect of MTG. It puts everyone on an even playing field, fighting with small decks and a set power level based on the card-pool, rather than how deep someone's pockets are.
This allows me to get very in-depth into the deck building, as I'm not just building a deck for me, I'm creating a custom set for people to draft with, create decks, find synergy and combos and ultimately have fun playing with. With the added benefit over other sealed formats like pre-release or draft that it's free to draft after the initial investment of creating the cube, of which I'm in a very fortunate position to own a lot of cards, so the intial investment was immediately offset by previous purchases of collections.
My CubeMy cube is located on CubeCobra, a website designed for creation, maintaining and discovery of different cubes. It is an aptly named Stuff on my Desk Cube for being created with what is available to me, rather than purchasing new cards to add in. It is fully balanced, 360 card cube. With 48 cards for each of the 5 colours, 6 dual coloured cards for each colour pair and 5 cards in each colour being dedicated to a specific theme supported by the colour pair, meaning 28 cards in each colour are just good stuff designed to fit in any deck in that colour.
This is fully outlined in my spreadsheet I made when designing the cube for the first time, this might be a bit behind the CubeCobra link, but I will endeavour to keep it updated alongside.