Doesn't solve the mobile apps part but we run https://passopolis.com/, a continuation of Mitro (https://www.mitro.co/) that shutdown a couple of days ago.

The server and the chrome/firefox extensions that are opensource (https://github.com/WeAreWizards/passopolis-server, https://github.com/WeAreWizards/passopolis-extensions).

Right now it's mostly for us and other mitro escapees to continue using it so we didn't bother with the site design or the mobile apps. The exact feature you mention would be the first one to be done if we decide to monetize it though ! It would say opensource as well.