If you don't believe this, look at how many major game releases now send out a free demo over the Net. Shareware is a way of selling your software. Generally, it works like this. You create a good computer program, good enough that people will pay for it. Then you split this program into two versions.
Some programs disable the save feature.
The demo is the version that is distributed over the net, generally for free. The other version is the full version, the complete program. It is not limited in any way and everything the program should be able to do is there. This is what the user who pays gets access too. Sometimes the full version is obtained by entering some sort of password into the demo version.