Fractal is a matrix client developed as part of the Gnome project.
It can be installed by getting the fractal package from the alpine repos.
Passwords are not saved
On some postmarketos installation, no keyring is created by default. This can be solved by downloading the seahorse package from alpine repos, pressing File > New > Password Keyring, and naming it login. You may have to use seahorse to unlock the keychain on each reboot, if your UI does not support unlocking keychains.