If your device is stuck in a boot loop (the device is crashing during boot, endlessly) after installing or updating applications, it is possible to recover from that by booting the device into Safe Mode which will disable all applications that are not part of the Replicant image.
Warning:
There is a bug #1986 which purges all accounts, including corresponding data, when booting into Safe Mode. Therefore, any not-yet-synced data (e.g. contacts, calendar appointments, etc.) which are bound to an account, as well as the account configuration itself, will be lost.
To boot into Safe Mode, press and hold down the "Volume Down" button during boot.
In fact it is enough to hold the button for approximately one second during the short vibration near the end of the boot sequence. It does not matter if the key was hold down all the time nor if other keys are pressed/held as well.
You will see a small dark box at the bottom left screen reading Safe Mode if you have been successful. Just reboot your device to disable Safe Mode again.