A simplified version which is cheaper to buy.
Software which is in the public domain.Anybody can use it without paying.
The full version with all the features.
You can try it for a while for free. Then if you want to keep using it, you are expected to pay a small fee to the writer.
You can use it for free for a while (often a month). when the trial period finishes, you have to pay, or the program will de-activate.