From what I see phplist is only free with the trial version.
After that they charge you per message or subscriber.
phplist
.com is a paid subscription service
vs
phplist
.org is open source php software (phpList is licensed with the
AGPL version3+.)
source:
https://www.phplist.org/about/How much does phpList cost?
phpList is free to download and run on your own servers. Running phpList effectively requires an appropriate hosting package and access to a working mail server, capable of delivering your campaigns. Even expert users will need help from time to time: community support is available on this website, including documentation and forums. Professional support is also available from experienced consultants and community members. phpList.com provides free hosted accounts and paid plans.
phplist
.org is what I linked to in my OP and every other place I've mentioned it.
phpList software is Open Source: this means you can use it for any purpose and you have the right to study, change and share the software.
phpList can be downloaded at
https://www.phplist.org/download-phplist/
