NickServ: Used to register and protect your nickname(s).
ChanServ: Used to register and protect your channel(s).
HostServ: Used to assign virtual hosts to your nick groups.
BotServ: Used to assign bots to channels.
MemoServ: Used to send and receive memos to/from registered users.
HelpServ: Used to print help informations about services commands.
DevNull: DevNull functions as a message sink. Any message sent to it will be ignored. It will not be logged, there will be no response. It will be lost forever. Whether it's useful or not is up to you; we just provide you with the option.