We are still actively working on the spam issue.
Coreboot
Coreboot is a Free BIOS replacement. Unlike libreboot Coreboot contains non-free blobs. This allows it to support a large number of motherboards.
Payloads
Coreboot by default use the simple as fuck SeaBIOS payload. Which is probably the closest thing to a stock BIOS. This payload supports a custom splash image. You can get some here They have to be saved in a weird way in GIMP[1]
The other payload that can be used is GRUB, this is used to have Full Disk Encryption. This is the payload libreboot use for their most releases.