There must be at least a dozen of these. The hard part seems to be getting people to scan and upload the photos, and then getting others to tag the people (and not being bought by Ancestry.com). One that seems to have hit a critical mass is https://www.wikitree.com/ - it has some interesting features I haven't explored yet, like 'free spaces' https://www.wikitree.com/wiki/Help:Free-Space_Profile