Contact
Tonttu is made by Volodymyr Linkevych, an individual developer in Cyprus.
Feedback, questions, problems: feedback@tontturemote.app
Or use Send feedback in the app (Help page): it drafts the email with the version numbers filled in and can attach a diagnostics file you can read first.
Security problems: security@tontturemote.app, privately, before publishing details. See the security policy.
Your data: what the app and the website do with it, and your rights, are in the privacy policy. Requests about your data go to the feedback address; I answer within a month.
No phone support and no office hours: it's one person, and email is the reliable way.