I run 1st edition Advanced Dungeons and Dragons, but with a LOT of house rules. They include: an alternate XP chart, a d10 individual initiative, spell points and an alternate spells/level chart.
Campaign Setting 1 "Aarenis"
The campaign world I have used for many years, Aarenis, is "home-written". In other words, it's a plagiarized patchwork with bits stolen from:
Elizabeth Moon's "Deeds of Paksenarrion" series (primary source of name, deities, culture and geography)
Glen Cook's "The Black Company" series and "The Tower of Fear" novel
Brian Daley's "Coramonde" series
Lois McMaster Bujold's "The Curse of Chalion"
Michael Moorcock's "Fortress of the Pearl" novel
The AD&D 2nd edition Al-Qadim Arabian Adventures Sourcebook
AD&D 1st edition and 3rd edition Oriental Adventures Sourcebooks
D&D d20/Legend of the Five Rings "Rokugan" books
Gods of Aarenis
Map of Aarenis
Geography of Aarenis
Aarenis Months and Holidays
Campaign Setting 2 "Midkemia"
Campaigns at Meetup
I considered using the Birthright campaign world as a setting and lost interest in it part way through editing it for my use. Mainly because it was too damn complex.