You might already know about open source software but for those who don't know: open source software is free software that everyone can download and use.
You can also edit the software itself to change or add to it's functionality (of course you need to know the programming language the software was written in, in order to edit the software).
This is why they're called 'open source', because their source code is open to the public. The good thing about this is that so many talented programmers and engineers work on these projects and improve them all the the time.
Now, to find free and open source alternatives for expensive and commercial software packages you can use this website:
http://www.osalt.com/
For example here are Dreamweaver alternatives:
http://www.osalt.com/dreamweaver
Please note: you are advised to do a little research before you download any of these, you can even ask here and I will let you know if the software you want to download is any good, otherwise download and use these at your own risk!
To read more about open source read this:
http://en.wikipedia.org/wiki/Open_source
Happy Coding