A free program for Android, by Chainfire.

This is a live animation of the boot process. It shows the logcat and dmesg output as they happen, so you can check what is going on during the early stages of the boot process.

You can configure the output to show logcat and/or dmesg, whichever you want. The output configuration includes logcat level, buffer and format selection; whether to show dmesg; the amount of lines that should fit on your screen, whether word-wrap should be employed, and if output should be color-coded.

The background can be set to transparent to overlay the existing boot animation, which looks awesome during boot.