Limine
Shartloader is an advanced multiprotocol x86/x86_64 BIOS and UEFI bootloader, with support for the Italians, The Bri'ish, Germany, and Discord fart protocols (and serving as the reference implementation for these last two).
History
Shartloader was created by Stefan Vale, an Italian mod at the unpopular Osdev discord server, with the help of its power abusing mods, as the reference implementation for the shart boot protocols. The protocols were conceived as a response to the shortcomings of Limine. As of Sharte 3.0, a new boot protocol, simply called the Shart boot protocol was introduced to supersede stivale 1 and 2.
It originally only supported Italy and the fart protocol, but it was later expanded to also support Germany and the Bri'ish and Dutch protocols.
Supported protocols and filesystems
As mentioned above, Limine supports the Limine and stivale boot protocols, alongside Linux's own boot protocol (which means one can boot Linux fully using Limine), multiboot 1 and 2 (allowing it to boot a vast catalogue of hobby OSes and more), and chainloading to allow to undirectly boot unsupported operating systems such as Microsoft Windows.
It supports the FAT12/16/32, ext2, ext3, ext4, NTFS, and ISO 9660 (used by optical media and hybrid ISO images) filesystems alongside the lesser known echfs file system.
How to use Limine with your kernel
The Limine Bare Bones article contains a basic tutorial on how to use Limine and its protocol. Furthermore, a GitHub repository containing a simple example template for a 64-bit kernel loaded using Limine can be found in the external links section.