Hello Patrick!
WiseMapping: https://bitbucket.org/wisemapping/wisemapping-open-source/src/develop/
You can try it on FramaSoft: https://framindmap.org
The FUSS distribution offers these tools:
- Freeplane: https://www.freeplane.org - Vym: http://www.insilmaril.de/vym/ - Vue: https://vue.tufts.edu/
Paolo.