Html editors presented below are open-source and runs on GNU/Linux, Mac OS X and Windows. Enjoy!
KompoZer
KompoZer is a complete web authoring system that combines web file management and easy-to-use WYSIWYG web page editing.
KompoZer is designed to be extremely easy to use,
making it ideal for non-technical computer users who want to create an attractive, professional-looking web site without needing to know HTML or web coding.
http://kompozer.net/
The SeaMonkey project
Web-browser, advanced e-mail, newsgroup and feed client, IRC chat, and HTML "WYSIWYG" editing made simple -- all your Internet needs in one application.
http://www.seamonkey-project.org/
Web Developer Extension
The Web Developer extension adds a menu and a toolbar with various web developer tools.
https://addons.mozilla.org/en-US/firefox/addon/60
FireBug
Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse.
You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
https://addons.mozilla.org/en-US/firefox/addon/1843
FTP - file transfer protocol - is a standard network protocol used to exchange and manipulate files from our computer to a web server.
FileZilla
FileZilla Client (also referred to as FileZilla) is a free, open source, cross-platform FTP client.
http://filezilla-project.org/
FireFTP
FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.
https://addons.mozilla.org/en-US/firefox/addon/684
http://fireftp.mozdev.org/