It is very useful , and includes an e-mail client , a calendar , a HTML editor , an IRC client , and a web browser . It is made by the SeaMonkey Council , formerly by Mozilla Foundation . SeaMonkey consists of a web browser ( SeaMonkey Navigator ) , which is a descendant of the Netscape family , an e-mail and news client program ( SeaMonkey Mail & Newsgroups , which shares code with Mozilla Thunderbird ) , an HTML editor ( SeaMonkey Composer ) and an IRC client ( ChatZilla ) .