The SeaMonkey 1 web browser was released on 30th January 2006. It is a part of an Internet suite which also has an email client and a WYSIWYG HTML editor.
SeaMonkey came into existence in 2005 when people at the Mozilla Foundation (which itself came from Netscape Communications Corp.) decided to work on standalone programs. FYI, the products that came out of Mozilla are the Firefox browser and Thunderbird email client.