Well, you can have multiple Operating Systems on the same computer system in two ways:
and to answer your question: any software that can be installed on a Host OS and can run, and possibly install also a Guest OS, will do.
VMWare can install a Virtual OS (Guest OS) and VMplayer (free of cost) can run a ready-to-use Virtual Machine that you create with VMWare.
To go (completely) free: use VirtualBox!
List these points here and I will help you setup your own Virtual Machine and install a Guest OS (Linux, for example) on it.
Free Hard Disk Space Available(you would need somewhere 5 to 8 GB):
LAN Card (also called NIC) Plugged in or not (most likely plugged in):
That way you can do Alt+ Tab or use your Mouse.
I do that! And who would not?