Two common categories for software according to copyright, and therefore with licenses that confer specific rights to the licensee, are proprietary software and free and open source software (FOSS). The obvious conceptual difference between the two is the granting of rights to modify and reuse a software product purchased by a client: foSS software concedes both rights to the customer and thus collects the modifiable source code with the software (“open source”), whereas proprietary software generally does not lay off those rights and therefore hide the source code (“closed source”). Many form contracts are only included in digital form and are presented to a user only as a click-through that the user must “accept.” Since the user may only see the agreement after the purchase of the software, these documents may be liability contracts. An example of a copyleft free software license is the GNU General Public (GPL) license, which is also the first copyleft license. The purpose of this license is to give and protect all users to unlimited freedom, to use, study and modify the software privately, and if the user complies with the GPL`s terms, to disseminate the software or make changes to it. For example, all changes made and retouched by the end user must contain the source code of these and the license for derivative works should not result in additional restrictions beyond what the GPL allows.  The most important effect of this form of license is that the end user must accept the software license if the ownership of the software remains in the hands of the software publisher. In other words, without the acceptance of the license, the end user cannot use the software at all. An example of such a proprietary software license is the license for Microsoft Windows. As with proprietary software licenses, this license contains a broad list of activities that are limited, for example.B.: reverse engineering, simultaneous use of software by multiple users, and the publication of repositories or performance tests.
End-user licensing agreements are usually lengthy and written in very specific legal language, making it more difficult for the average user to give informed consent.  When the company designs the end-user licensing agreement in such a way as to deliberately deter users from reading it and is difficult to understand, many users may not give their informed consent. One of the main consequences of open source licensing is that acceptance of open source licenses is essentially optional – the end user can use the software without accepting the license. However, if the end user wishes to exercise one of the additional rights granted by an open source license (for example. B the right to relay the software), the end user must accept the license of the software and be linked to it. An end-user license agreement (EULA, /-ju-l/) is a legal contract between a software developer or provider and the user of the software, often acquired by the user through an intermediary such as a distributor.