Single user Software: It means the software that cannot be shared between users.
Multi- User Software: It is software that can be used between users and multi users can share it.
Open Source Software: Open-source software is computer software that is available with source code: the source code and certain other rights normally reserved for copyright holders are provided under an open-source license that permits users to study, change, improve and at times also to distribute the software.
The legal requirements for:-
Single User Software: The single user of software it is copyright protected or with license so it cannot be copied or used by another user without permission.
Multi- User Software: This sort of Software can be used by multi- Users only or group of users like company or organisation and it is copyrighted to the company only it is illegal to be used by others.
Open Source Software: This Software is permitted to copyright holders and to those users who has access to it for editing and it has policy like term and condition so the users should follow these terms even if it is open Source.