Plymouth is described as 'application that runs very early in the boot process (even before the root filesystem is mounted!'. There are 2 alternatives to Plymouth for Linux. The best alternative is xsplash, which is both free and Open Source.
The list of alternatives was last updated Apr 7, 2016
xsplash is a software project in the Ubuntu community that uses the X Window System to replace the scrolling-text screens that appear while booting a Linux-based computer with a... View 2 alternatives to xsplash