If, on the other hand, you don't like the software, you can just Trash it. It's as easy as that. There are all kinds of variations on these basic themes. Some companies make demos of their software available. These may be fully functioning or limited in some way.
Some authors ask for a postcard, email or charitable donation rather than money.
Nagware will nag you to pay. You might find some kind of time delay built in so that you can't start using the software or click a button until you've seen a reminder screen for a few seconds. Sometimes the software is limited until you pay. After paying you will receive a passcode whch unlocks the software are then you can use all the features. Looking for Software There are many many sources of excellent shareware and freeware for the Mac.