I recently tweeted that QCAD is all the CAD I want. I only need 2D, it’s keyboard friendly, cross platform and the default file format is DXF, which is compatible with everything and text based so git likes it (although I wouldn’t want to diff/merge one).
Anyway, it doesn’t come with a .desktop file for unity/ubuntu, so I knocked one up, which I published as a Github gist.
By default, qcad is installed by just unpacking into /opt/qcad[…]/ and run from the command line. If you drop the desktop file into either /usr/share/applications/ (for all users) or ~/.local/share/applications for the current user (create the folder if it doesn’t exist). You should then be able to find the icon/launcher in unity, and be able to pin it to the sidebar if you wish.