What private alternative to google forms would you recommend?

Ideally something that does not require respondents to log in. Thank you!

Every client I support who's open to ditching Google apps has one indispensable requirement of any replacement of Google apps: They must be able to view their Google, Microsoft, and Google-replacement accounts in the same OS-native mail, contacts, and calendar apps. This serves two purposes:

1. They need to see their personal and work communications and schedules in the same window. This is essential, for example, to avoid double-booking themselves.
2. They need to be able to gradually transition between their old personal accounts and their new, as they update contact information with one person, business, nonprofit, and government agency at a time.

For #E2EE services, this requires a local SMTP, IMAP, CalDAV, and CardDAV bridge (or, for mobile devices lacking support for this, a self-hosted bridge server and a VPN to which).

What options provide this capability?

Missing: in the Android category please also consider alternatives which are not derivatives of AOSP (of the open source parts or android), i.e. mobile GNU/Linux distros such as:
- SailfishOS
- PostmarketOS
- UbuntuTouch
etc.

SFOS is definitely daily driveable: I am posting from a phone running it.