Resources
2P-Kt
tuProlog
social
The two implementations carry different licences.
2P-Kt — Apache 2.0
The Kotlin ecosystem is open source software, released under the Apache 2.0 License, which allows commercial derivative work.
Details on the 2P-Kt pages.
tuProlog — LGPL
The Java engine is released under the GNU Lesser General Public License — LGPL 2.1 for the early versions, LGPL 3.0 from version 2.8 on — which allows commercial derivative work as well.
Details on the tuProlog pages.