KAD is a complete 2D CAD system based on QCad by ribbonsoft.
KAD is available under the GNU General Public License, version 2. The KDE adoption is written by Martin Teichmann, who is not related to ribbonsoft (therefore don't blame them for bugs).
Until now, KAD can only be considered alpha software, unstable, lacking functionality. For the KDE user interface part that is, as QCad is already a production quality CAD system, the CAD part is actually very stable.
As KAD is a KDE program, KDE3 and Qt3 must be installed on your machine, including the developer packages, in order to compile KAD. KAD uses cmake for compiling.
Once you have unpackaged the source package, you should create a new directory in which you compile, and in this directory you start cmake and then make. Or in short:
tar -xzf kad-0.8.0-src.tgz
where the last line is to be executed as a root user in order to install KAD system wide.