Take a look at Crowdsource Reporter. It allows the public to report issues on desktop or mobile devices without having to download any apps or log in anywhere. Survey123 also allows for public input and could be just in the browser (no app download). You can also create your own mobile apps with App Studio, though I don't personally have experience with it. At this time, Collector does need a named user from an organization, so we use it for internal use only. Organizations should not be allowing users to share a named user account per ESRI policy.
Thanks for the update, Crowdsource does look useful. As an update to my original post, a lot has change in 4 years, and due to laws and licensing, we have to go through a lot of flaming hoops to enable public data collection. The documentation has since clarified the question.Regarding your latest post, I'm a big fan of S123, and have grand visions to use the web page version of it for a very neat and cool public ####### reporting application. Stay tuned......
ArcGIS Field Maps is now the best option for data collection without an AGOL account.