Follow these steps to run multiple instances of Skype on same machine.
Windows
- 
    From the Windows taskbar, click Start > Run (or press the Windows  + R keys on your keyboard at the same time). + R keys on your keyboard at the same time).
- 
    In the Run window, type the following command (including the quotes) and press Ok: - For 32-bit operating systems: "C:Program FilesSkypePhoneSkype.exe" /secondary
- For 64-bit operating systems: "C:Program Files (x86)SkypePhoneSkype.exe" /secondary
 
- For 32-bit operating systems: 
Linux
- Press Alt + F2 and type the following command: skype --secondary
- Alternative : Open a terminal and use the following command in it: skype --secondary &
Mac
- Use this command in terminal: sudo /Applications/Skype.app/Contents/MacOS/Skype /secondary