The Internet Archive is celebrating its 25th anniversary.
https://anniversary.archive.org/
That’s older than both Sensei’s Library (2000) and Wikipedia (2001), as well as all living Go servers (I think) except IGS (1992). Probably a similar age to rec.games.go, but we can’t really call rgg alive any more.
By the way, Wikipedia disagrees with the popular idea that the Library of Alexandria was totally burnt:
Despite the widespread modern belief that the Library of Alexandria was burned once and cataclysmically destroyed, the Library actually declined gradually over the course of several centuries. This decline began with the purging of intellectuals from Alexandria in 145 BC …
The Library, or part of its collection, was accidentally burned by Julius Caesar during his civil war in 48 BC, but it is unclear how much was actually destroyed and it seems to have either survived or been rebuilt shortly thereafter; the geographer Strabo mentions having visited the Mouseion in around 20 BC …
The Library dwindled during the Roman period, due to a lack of funding and support. Its membership appears to have ceased by the 260s AD. Between 270 and 275 AD, the city of Alexandria saw a Palmyrene invasion and an imperial counterattack that probably destroyed whatever remained of the Library, if it still existed at that time.