In case anyone else was wondering, this doesn't seem to be the same thing as the Planner app of Gnome: https://wiki.gnome.org/Apps/Planner

(Gnome's Planner doesn't look like it's being developed at the moment, but it's a pretty decent tool in the style of old-school Microsoft Project. The files are also pretty git-friendly. I'd actually been thinking of moving back to it, since it's lower friction to edit than Instagantt, and also lets one assign multiple resources to a task.)