Since basically all chat apps pretend to save the data encrypted (they dont). I wanted an easy and convenient alternative. The chat server at threema has no storage and works since 13 years on an old ruby script. Since Gateway costs money and account creation is paywalled behind platform DRM (Apple Appstore / Google Play Store). The only right solution is to (miss)use the existing multi device functionality via qr code linking. Thanks to codex for helping me with this.