The most games are available in PGN Format . This format can be viewed or imported in Scidb.
Mark Crowther's The Week in Chess is providing daily chess news and games. Furthermore this site provides chess archives with high quality.
The site Now In Chess by Gerardo Fernandez is tracking games of high quality not contained in TWIC archives. But it seems that this page is abondened.
FICS is providing a huge archive with Internet games of different variants: Normal chess, Chess 960 (wild/fr), Giveaway Chess (wild/26), Losers Chess (wild/17), Three-check Chess (wild/25), Bughouse (wild/24), and Crazyhouse (wild/23).
"PGN Mentor" provides PGN archives of individual players and different tournaments .
365Chess.com provides an opening explorer and allows to search for games in the database.
Many chess engines are available. A good listing is provided by CCRL 40/40 , which allows an overview over the strength of the engines.
Of particular significance are:
Scid is probably the best known free chess database, originally developed by Shane Hudson. The today's version of Scid is rather buggy.
Scid vs. PC , maintained by Steven Atkinson, is a bug-fixed version of Scid, with focus on greater usability.
Gerhard Kalab's Scid on the Go lets you use Scid for an Android tablet.
ChessX , currently developed by Jens Nissen, provides a free chess database specialized on the PGN Format .
No longer in development, but still of interest, is the Java application José .
A quite useful page with links about chess history, rules, strategy and tactics, and more, is Car Games: Chess.