The Legal Sets are: Alpha, Beta, Unlimited, Revised, Arabian Nights, Antiquities, Legends, The Dark, Fallen Empires, Collector's Edition, and International Collector's Edition. All reprints of those cards with the original art and original border are also allowed.
Each deck must contain at least 60 cards and be singletons (i.e. not more than one of any card) with the exception of basic lands. There are no sideboards in Old School Singleton.
The following cards are banned in Old School Singleton:
Ring of Ma'rûf is legal, but you may only use it to get a card that is legal under the above rules and that you do not already have a copy of in your deck.
Chaos Orb and Falling Star have the same (updated) errata as set forth by Eternal Central rules