What are the open source equivalents to the following

Windows-Linux
Adobe Photoshop-Gimp
Office-Star Office
Dreamweaver-NVU/Aptana/konqueror

What is open source software?

Open Source is a software that is released with source code under a license that ensures that derivative works will also be available as source code, protects certain rights of the original authors, and prohibits restrictions on how the software can be used or who can use it.
Its impact on Microsoft is not good because people can download free programs instead of buying them.
The impact on my wallet is nothing because it costs free and there is no need for me to spend money when i could just download it for free.