A brief summary of the GPL (AGPL) license
Since I am mainly engaged in web system development, my knowledge of licenses is limited. However, I had an opportunity to investigate the GPL license and AGPL license, and I have summarized the results of my research.
GPL License and AGPL License
The GPL license is based on the concept of copyleft.
The idea is that if you use a GPL-licensed library, your original application should also be GPL-licensed (OSS-ized and source code disclosed).
If commercial software that is installed and distributed uses GPL-licensed libraries, it is fine for the commercial software to be GPL-licensed as well, but if an original application that uses GPL-licensed libraries via a network such as a web system uses GPL-licensed libraries, the source code must be made public because the software is not being distributed. However, if you use GPL-licensed libraries in your own networked applications such as web systems, you do not need to disclose the source code.
The license corresponding to this loophole is the AGPL license (Affero General Public License).
The iText license explanation is easy to understand. iText has been AGPL licensed since Series 5.
Under the AGPL license, you cannot deploy your own applications on the network without releasing the complete source code for them. You must distribute all source code, including proprietary products and web-based applications.
The AGPL wiki describes copyleft for ASP (SaaS).
To solve the problem that the copyleft clause in GPLv2 does not apply to ASP, Affero, Inc. created AGPLv1 in March 2002, and the Free Software Foundation created AGPLv3 on November 19, 2007. Both are strong copyleft licenses with copyleft clauses that apply even to ASPs. AGPLv3 is a highly trusted software license endorsed by the Free Software Foundation, the Open Source Initiative, and the Debian Project.
Even for web systems (ASP, SaaS), if you are using AGPL-licensed libraries, the AGPL license requires you to disclose the source code.