@fembot --
First off, you need to understand what it means to be "Open Source."
This is a "Class" of software denoting software for which the original source code is made freely available and may be redistributed and modified.
That's it. After that point, most Open Source software lean on specific licensing. Open Source software utilize "Copyleft" and "Permissive" licensing, mostly.
Mastodon utilizes GNU Affero General Public License. https://en.wikipedia.org/wiki/GNU_Affero_General_Public_License
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GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.