Here is a list of all files with brief descriptions:

Buffer.h
Chan.h
Client.h
Config.h
Csocket.h
defines.h
ExecSock.h
FileUtils.h
HTTPSock.h
IRCNetwork.h
IRCSock.h
Listener.h
main.h
MD5.h
Message.h
Modules.h
Nick.h
Query.h
Server.h
SHA256.h
Socket.h
SSLVerifyHost.h
Template.h
Threads.h
Translation.h
User.h
Utils.h
version.h
WebModules.h
znc.h
ZNCDebug.h
ZNCString.h