Pencil and Paper Games is devoted to games you can play with nothing more than a pencil and a piece of paper (some of which can be played on the site, for those who do not have access to a pencil and paper, or remember what those are.) [more inside]
How I invented games, and why not - an essay by game designer Christian Freeling. Between 1979 and 1986 I invented some fourty abstract games, most of which can be found in the ArenA and the Pit. Dameo, HanniBall, YvY and Symple(x) are exceptions. Dameo's invention in 2000, after an incubation period of fifteen years, took two minutes. The invention of HanniBall and YvY in 2009 and Symple and Lhexus in 2010 were 'live' occurences decribed in a late arrival and a final whisper respectively. Looking back now, from a safe distance, and with the benefit of hindsight, I'd like to clarify how and why I invented these games, and more specifically why not...
Elves Under Hoof (direct link to a zipped file of four PDFs) is a free print-and-play solitaire game from Dan Verssen. From the rules: Victory: You win when the last elf is dead. You achieve a Prancing Victory if you have 5 or more surviving reindeer. You get a Spoiled Meat Victory if you have 2 or less surviving reindeer. You lose if all your reindeer are killed and left to rot in the snow. It is included, naturally, in the Games involving Elf Death list at BoardGameGeek.
LiveDosGames is a free, portable, fast Linux Operating System, which contains old, but legendary Dos games (and fits on a USB stick)
Walter Randelshofer's Pretty Patterns collection (for Rubik's cubes up to 5x5x5) is one of the nicest twisty puzzle sites going. It's based on his CubeTwister software, which you can download (including a lovely OS X standalone). If you really want a treasure trove of twisty polyhedra, check out gelatinBrain's enormous collection of java applets (which unfortunately don't do so well on macs). Are those things even physically possible? Really? Mini bonus: Randelshofer also hosts an archive of fondly-remembered Amiga animations.
Rocks 'n' Diamonds for some Friday puzzle-game fun. Described as "in the tradition of" Boulderdash and Sokoban, it's actually a superset of both, and you can waste tons of time playing all the old familiar levels or tons of others. (It's a quick download, for linux/os x/the other thing.)
Kurnik is a (free) online game site - bridge, chess, go, hex, that sort of thing - that's been established for years but only recently launched an English-language version. It seems notable among the many many many online game sites for lightweight, clean, ad-free design. The games are java-based.
Phutball (Rules, Java Applet), aka Philosophers' Football or ConwayGo is a deceptively simple 2-player game you can play on a Go board, or any rectangular grid. (It may be simple, but finding the right move is [PDF] NP Complete.)
Bunnock - a game of skill, accuracy... and horse bones. Register your team for the world championship!