Answering your questions in reverse:
Also is there a free version of vmware?
As mentioned by others VMWare Player is a free version of VMWare for desktops and other providers also have various solutions.
What are some other uses for this technology besides multiple OS's?
Obviously one of the biggest uses for virtual machines is to run multiple OS's but it can also be used to just run multiple INSTANCES of the same OS (eg. you could have Windows 7 as your host OS and as a Guest Virtual Machine). As to why you would do this a good list of uses is shown in: 7 Uses For a Virtual Machine which list:
- Try new operating systems
- Test your software
- Set up an office quickly
- Small Biz disaster recovery
- Build kid boxes
- Backup your system
- Save Legacy Systems
Another one i can think of is to have a very 'clean' empty host and put all your installed stuff on your guest and use snapshots so it is easier to backup if something goes wrong or allow you to test things as mentioned.