Apps similar to ZWOOKY include Proton Mail, which is open source with a free version. Other options are Vivaldi Mail, Kolab Now, mail2world and Safe-mail.net. In total there are six WebMail Providers like ZWOOKY for the web, Android, iPhone, iPad and Mac.
Proton Mail provides secure email services with end-to-end encryption, ensuring data protection. Swiss-based and outside US jurisdiction, it offers a free version to champion privacy as a human right. Fully accessible on any device.
Switzerland
Vivaldi Mail is a free email service with no ads and no strings attached developed by Vivaldi Technologies. It also offers contacts and calendar features, search capabilities, folders management, WEB/POP/IMAP access, 10GB of storage capacity, 20 MB of maximum attachment size...
Norway
Kolab Now provides a suite of intuitive apps in a user friendly environment to make your day to day online comms easier, smarter and most importantly; secure.
Switzerland
High security web-based e-mail system which extends considerably the email system to much more than currently exists.
United States
South Africa