Editing Application software (section)

=== By property and use rights ===
Application software is usually distinguished into two main classes: closed source vs [[open source software]] applications, and [[free software|free]] or [[proprietary software]] applications.

Proprietary software is placed under the exclusive copyright, and a [[software license]] grants limited usage rights. The [[open-closed principle]] states that software may be "open only for extension, but not for modification". Such applications can only get [[Plug-in (computing)|add-ons]] from third parties.

[[Free and open-source software|Free and open-source software (FOSS)]] shall be run, distributed, sold, or extended for any purpose, and -being open- shall be modified or [[reverse engineering|reversed]] in the same way.

FOSS software applications released under a [[free license]] may be [[List of countries' copyright lengths|perpetual]] and also [[royalty-free]]. Perhaps, the [[ownership|owner]], the [[holder (law)|holder]] or third-party [[law enforcer|enforcer]] of any right ([[copyright]], [[trademark]], [[patent]], or ''[[ius in re|ius in re aliena]]'') are entitled to add exceptions, limitations, time decays or expiring dates to the license terms of use.

[[Public-domain software]] is a type of FOSS which is royalty-free and - openly or reservedly- can be run, distributed, modified, reversed, republished, or created in derivative works without any [[attribution (copyright)|copyright attribution]] and therefore [[revocation]]. It can even be sold, but without transferring the public domain property to other single subjects. Public-domain SW can be released under a (un)licensing legal statement, which enforces those terms and conditions for an indefinite duration (for a lifetime, or forever).