Threema is a mobile messaging app that puts security first. With true end-to-end encryption, you can rest assured that only you and the intended recipient can read your messages.
Unlike other popular messaging apps (including those claiming to use encryption), even we as the server operator have absolutely no way to read your messages.
Here you can purchase Threema for Android without going through the Google Play store. We recommend that you use Google Play if possible, as it will allow you to get automatic updates. This shop is only intended for those users who cannot use Google Play.
site link: https://threema.ch/shop/