Legal Definitions - copylefted software

Copylefted software refers to computer programs distributed under specific licensing terms designed to ensure that the software, and any modified versions derived from it, remain free for others to use, modify, and distribute. While not a formal legal term, "copyleft" is a concept used to describe licenses that leverage copyright law to achieve the opposite effect of traditional proprietary copyright: instead of restricting user freedoms, it guarantees them. These licenses typically stipulate that if the software is redistributed, either in its original form or after modifications, it must be accompanied by the same or equivalent licensing terms, preventing anyone from adding new restrictions or making the software proprietary.

• Example 1: A Developer Building a New Application

  Imagine a software developer creating a new productivity application. To incorporate advanced data visualization, they decide to use a powerful charting library that is licensed under a copyleft agreement, such as the GNU General Public License (GPL). Because they are integrating this copylefted library into their new application, the developer is obligated to distribute their *entire* productivity application under a compatible copyleft license if they choose to release it to the public. They cannot simply use the library and then sell their application as proprietary software with restrictive terms, as the copyleft license "flows through" to the derivative work.

• Example 2: A Company Customizing Software for Clients

  A small tech company decides to customize an existing open-source content management system, which is copylefted, to create a specialized version for their e-commerce clients. They add new features, optimize performance, and integrate unique payment gateways. When they distribute this customized content management system to their clients, the copyleft license requires them to also provide the source code for their modifications and allow their clients the same freedoms to use, modify, and redistribute that version. The company cannot simply distribute the modified system as a closed-source product without adhering to the original copyleft terms.

• Example 3: An Individual Sharing a Modified Utility

  Consider an individual who finds a copylefted command-line utility for managing system files. They decide to modify it to add a new function that automates a specific backup process they need. If they then share this enhanced version of the utility with friends or upload it to a public repository, the copyleft terms of the original utility dictate that their modified version must also be distributed under the same or a compatible copyleft license. This prevents them from taking the original free software, making improvements, and then claiming exclusive ownership over their enhanced version.