PLAYER DATA files a player has on his hard disk while playing his turn; TRN FILE describes the TRN file format in all its variations; RST FILE describes RSTs; HOST DATA describes the files the Wisseman Host (and PHost, though -- strictly speaking -- PHost is "3rd party") uses to keep universe data and other information; FIXED DATA files that are normally constant throughout a game, such as the xxxSPEC files or name lists. These are used by the host and the players; CHECKSUMS lists all checksums you may need to update if you write a player-side program; 3rd PARTY file formats of various 3rd party programs (not by Tim Wisseman). If you wish your file format to be added here, feel free to contact me. There's a client-side section and a host-side section; FILE LIST a list of file names and programs that own these files. Comes in handy when debugging game directories people sent you; FIELD LIST provides a cross-reference about which property is stored where.
Note that the borders between sections are floating: what you consider a host file, I may list under `fixed' or even `3rd party'.