This is a place where copyright law and theory still haven't quite caught up, though there are numerous attempts to make laws about these things while just ignoring facts like "To use software one must often copy a significant part of it into memory".
ETA: There's usually something about being allowed to make copies of software if it "is an essential step in the utilization of the computer program", which is arguably an extension of the "transitory duration" clause (which would cover the 'mirror' case)
One of my long-standing interests is in writing content that will age gracefully, but as a child of the Internet, I am addicted to linking and linkrot is profoundly threatening to me, so another interest of mine is in archiving URLs; my current methodology is a combination of archiving my browsing in public archives like Internet Archive and locally, and proactively archiving entire sites. Anyway, sites I have previously archived in part or in total include:
Having recently added WikiWix to my archival bot, I was thinking of re-running various sites, and I'd like to know - what other LW-related websites are there that people would like to be able to access somewhere in 30 or 40 years?
(This is an important long-term issue, and I don't want to miss any important sites, so I am posting this as an Article rather than the usual Discussion. I already regret not archiving Robert Bradbury's full personal website - having only his Matrioshka Brains article - and do not wish to repeat the mistake.)