Corresponding source
Publishly is built on the open-source Postiz engine & is licensed under the GNU Affero General Public License v3.0 (AGPL-3.0). Under section 13 of that license, everyone who uses this service over the network is entitled to receive the complete corresponding source of the version that is running.
The source of the currently deployed revision is available here: https://github.com/PhliqOG/publishly.
License
The full license text ships with the source tree (LICENSE), together with a compliance guide (LICENSE-COMPLIANCE.md) describing exactly which obligations apply to operators of this software.