• Copyleft software - free software whose derivatives and copies must also be distributed as free software.
  • Non-copyleft free software - Free software whose license allows derivatives to be turned into proprietary software.
"The Free Software Foundation follows the rule that we cannot install any proprietary program on our computers except temporarily for the specific purpose of writing a free replacement for that very program. Aside from that, we feel there is no possible excuse for installing a proprietary program."
  • Freeware - generally refers to software that is distributed free-of-charge, usually in binary. Not the same as free software.
  • Shareware - allows users to share applications with others, but it does not include the source code and usually requires users to pay a fee if they continue using it.