OSM has a heatmap feature. Users can contribute tracks and feed into it:

Awesome! Thanks. I'll look into it.

Edit: hmmm I don't think I understand that wiki. Most of those are not the type of heatmap I was thinking of. I'll keep looking into it though.

	▲	stigi 4 minutes ago \| parent [-]
		In fact they are called "Public GPS Traces" and can be enabled in the OSM layer inspector. I am not sure if anyone started distilling track recommendations from them yet though. Here's a link that has traces enabled (aka layer "G"): https://www.openstreetmap.org/#map=15/52.47166/13.40590&laye... There's also a list of recent uploaded traces: https://www.openstreetmap.org/traces