Con No longer offically licenced with a GPLv3+ version
In 2014 Quasado released Gravit.io having dual licensing: GNU GPLv3+ or a commercial license. This effectively made Gravit.io opensource, when they transitioned to "Gravit designer" they essentially dropped GPLv3+ license.
You can still get the GPLv3+ licensed version of Gravit.io here: https://github.com/OliBridgman/gravit
You can read the GPLv3+ licensing here: https://www.gnu.org/licenses/gpl.html