Here are the classes, structs, unions and interfaces with brief descriptions:

CAuthBase
CBlowfish	Does Blowfish w/64 bit feedback, no padding
CBuffer
CBufLine
CChan
CClient
CClientAuth
CConfig
CConfigEntry
CCron	This is the main cron job class
CDebug
CDebugStream
CDir
CException
CExecSock
CFile
CFPTimer
CGetAddrInfo	This function is a wrapper around getaddrinfo (for ipv6)
CHTTPSock
CIncomingConnection
CIRCNetwork
CIRCSock
CListener
CMD5
CModCommand	A helper class for handling commands in modules
CModInfo
CModule	The base class for your own ZNC modules
CModules
CModulesIter
CNick
CPerlModule
CPerlSocket
CPerlTimer
CPyModule
CPyRetBool
CPyRetString
CPySocket
CPyTimer
CRealListener
CSCharBuffer	Ease of use self deleting char * class
CSConnection	Options for creating a connection
CServer
CSListener	Options container to create a listener
CSmartPtr	This is a standard reference counting pointer. Be careful not to have two of these point to the same raw pointer or one will be deleted while the other still thinks it is valid
CSMonitorFD	Class to tie sockets to for monitoring by Csocket at either the Csock or TSockManager
Csock	Basic socket class
CSockCommon	Simple class to share common code to both TSockManager and Csock
CSocket	Base Csock implementation to be used by modules
CSocketManager	Best class to use to interact with the sockets
CSockManager
CSSockAddr	Sockaddr wrapper
CSSSLConnection
CSSSListener
CString	String class that is used inside ZNC
CTable	Generate a grid-like output from a given input
CTemplate
CTemplateLoopContext
CTemplateOptions
CTemplateTagHandler
CTimer
CUser
CUtils
CWebSession
CWebSessionMap
CWebSock
CWebSubPage
CZNC
CZNCSock
CZNCTagHandler
MCString	A dictionary for strings
MCString_iter
md5_context
PString
sha256_ctx
String
TCacheMap	Insert an object with a time-to-live and check later if it still exists
TSocketManager	Ease of use templated socket manager