Here is a list of all documented files with brief descriptions:

[detail level 12345]

include
steamclient
connections
connection.hpp	Abstract transport interface used by the Steam networking layer
tcp.hpp
crypto
crypto.hpp
helpers.hpp
external
ctljson.hpp
network
cmclient.hpp
routing
commands
register.hpp
router.hpp
events
dispatcher.hpp
register.hpp
table.hpp
types
generated
SteamLanguage.hpp
SteamLanguageInternal.hpp
clientmsg.hpp
msgbase.hpp
packetbase.hpp
utilities
msg_utils.hpp
stream.hpp
vdf.hpp	Minimal representation and parser for Valve Data Format (VDF)
client.hpp	Steamworks minimal C++ wrapper
events.hpp	Event and command definitions used by the Steam messaging layer