Skype
Skype can be installed from the official Ubuntu repositories however, you'll firstly need to enable the Canonical Partners repository.
To enable the Canonical Partners repository, open System Settings > Software & Updates and on the "Other Software" tab, click the box next to "Canonical Partners":
... and make sure you click "Reload" when asked about reloading the information about available software.
then install it from the command line, using
sudo apt-get install skype
Also fix Skype on 64bit not using the correct theme, by installing the missing dependencies using the following command:
sudo apt-get install gtk2-engines-murrine:i386 gtk2-engines-pixbuf:i386
The use of the internal microphone sometimes goed wrong. To change that install the pavucontrol
sudo apt-get install pavucontrol
and make sure the input/output is set to Audio Stereo Duplex or Microphone unplugged. On some systems it might have another name. Skype soemtimes doesn see other microphones available in the system. After correcting the input to another Microphone I could here myself in a Skype test call.
In the dutch version on my ACER C720P chromebook running Ubuntu 16.04 it looks like this: