I really like MakerCAM, and its even possible to use MakerCAM offline.
1. get the stand alone version of adobes flash player http://www.adobe.com/support/flashplayer/downloads.html
2. get the makercam.swf file, with linux just type in your terminal
wget http://www.makercam.com/makercam.swf
on windows just use a download manager and download the swf file.
3. Start the stand alone version of adobes flash player and drag and
drop the swf file into it.
4. Use it offline.
It's on-line i don't trust the cloud. For private work.
So don't use this as a main tool.
OK for FREE, good for trying.
Good for learning.
Nice resource for the student.