FREE/NOSTALGIA GAMES

DOS Games - play free in your browser; full screen capable (on archive.org)
Internet Arcade - old computer games (on archive.org)
8bit Workshop - Write your own 8-bit games and see them run instantly within your browser

INTERNET 1.0

Principia Cybernetica Web - A collection of writing and philosophical works from various scientists and thinkers including subjects like global intelligence and cybernetics created in 1993
The Man in Seat 61 - Website with detailed information on passenger trains worldwide from a man who has ridden on each of them in seat 61
Pictures From Old Books - Over 3800 pictures antique books as old as the 1400s, scanned from the collection of an individual book collector
Insecure.org - Personal site of Fyodor, a prominent figure in early web hacking and current web security
Earth Conditions - Global animated map of wind, weather, and ocean conditions
Every Noise At Once - A library of sounds
Astronomy Picture of the Day - a new picture posted daily by NASA
100,000 stars - explore our galactic neighborhood
Mandelbrot Set Viewer - explore some pretty fractal geometry
Windows 93 - Emulate Windows93 in your browser
Esref Armagan - Paintings by a man born blind

ARCHIVES

Internet Archive - an archive of games, programs, books, tv, etc. from the past
Internet Wayback Machine - search for screencaps of long dead websites (part of the internet archive)
Webdesign Museum - Archive of iconic webdesigns from different eras
Usenet Newsgroup Archives - Links to various archives going back years

LEARNING & EDUCATION

CNX.ORG - learn anything! large online database of textbooks and courses
The World Wide Web Virtual Library - online since 1991

VIDEOS

Strandbeest - Wind-powered "beasts" that roam the shores of the Netherlands
Wintergatan Marble Machine - Music Machine powered by marbles
Life of the Cosmos - 2 minute video showing the evolution of the universe

AID SCIENTIFIC PROGRESS

SETI@home - scan the skies for extraterrestrial life
CureCoin - earn cryptocoins while you fold proteins for medicine and biology