We are adding support for sharing view/edit links to existing entries in Cognito Forms in the next two weeks. You can already enable Save & Resume to support saving progress and resuming later before submitting entries.
This feature takes this capability way further by allowing you to include secure links on the confirmation page, confirmation emails, and shared when managing entries that allow anyone to view and/or edit individual entries without logging into Cognito Forms. You can also use conditional logic to automatically disable these links to support your internal workflow processes.
https://trello.com/c/pbrbGrft