Crowdmap allows the investigator to set up a Web map around a particular topic and invite multiple users (participants, research subjects, collaborators, multiple assistants) to contribute information to the map on their own time and from their own device.
For $10/month, users can buy fee-based services including private maps and custom branding.
Users have complained that Crowdmap is glitchy and unreliable. It is hard to find recent examples of successful projects built with the app. There is no other free and open source tool that fills the precise niche. For a freemium closed source service that allows crowdsourced point data only, try ZeeMaps. For a fee-based, open source crowd mapping tool, try the shared tables function of CartoDB.