Some quick summations of some of the most common:
Commercial: Must pay for the software, you may not distribute it, in most cases you cannot reverse engineer it or modify it, you may not make copies of it, possibly you may not use it for financial gain without express consent of the author, etc.
Shareware: Can be used without cost, but the authors may request compensation if used beyond a certain time limit.
Freeware: No cost to use, but the authors retain all copyrights.
Adware: Free to use, but you must leave the advertisement components installed to use the software.
Cardware: Free to use, but the user wants you to send them a postcard from wherever you live.
GNU public license (often called "open source"): You may use the software without cost and modify it at will. You can also modify it and resell for financial gain, but if you distribute the modification for financial gain you must make the source code of your modification freely available to the public and your modification is to be made available under the same GNU terms as you received it.
Copyleft: The author has made the software freely available to the public and has retained no copyrights for themselves, nor have they imposed any use/modification/distribution restrictions on subsequent users. Basically, to release it to the Public Domain.
Creative Commons license: "You let others copy, distribute, display, and perform your copyrighted work" but with possible restrictions like no derivatives allowed, no distribution for financial gain, must make derivatives available under the same type of license, must always give the author credit.
Josh
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