The purpose of this post is not to encourage the software piracy, but just spreading the knowledge.
Today there are many applications and software available on the Internet, which have great utility and are distributed as demo software. The developers of these demo versions usually disable some of the important features of these software. If you want to use these features, then you have to pay for buying the complete version.
Another method used by the developers is to allow users to use the software only for a limited period after which these software get expired an you have to again pay for continuing using that. The purpose of both these methods is to get you addicted to using that software and then ask you the money.