I have plugged Qcad here before. http://www.qcad.org/en/qcad-documentation/qcad-features has a list of features for both the free and the professional version. I uses the free one for a couple of years, but then I finally broke down and bought the pro version. It is a fairly simple 2D program that feels mostly like pen and paper. The Pro version runs about $45 for just the software or $72.50 with an e-book. I can't say much about the book since I never seemed to need it. One nice thing about qcad is that it runs on Windows, Mac and Linux, so whatever way you like to run your computer, it should work ok. It even has a feature that lets you contruct an iso view from your regular views.
Here is a sample of something I am woking on right now:
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I going to try it on this laptop. I still sketch out my ideas on paper. Cad for me is more of a curiosity. I admire those who can take the time to use it correctly. To those designers THANK YOU for sharing your ideas and designs with us.