mkbootimg, unpackbootimg:
https://github.com/CyanogenMod/android_system_core/tree/cm-10.2/mkbootimg (initial sources)
https://github.com/huaixzk/unpackbootimg (makefiles)
https://github.com/osm0sis/mkbootimg (patches)

pxa-mkbootimg, pxa-unpackbootimg:
https://github.com/AKuHAK/pxa-mkbootimg (initial source)
https://github.com/osm0sis/pxa-mkbootimg (patches)

elftool:
https://bitbucket.org/srl3gx/elftool (initial source)
https://github.com/osm0sis/elftool (patches)

unpackelf:
https://github.com/tobiaswaldvogel/and_boot_tools/tree/master/bootimg (initial source)
https://github.com/osm0sis/unpackelf (patches)

mboot:
https://github.com/osm0sis/mboot

dumpimage, mkimage:
https://www.denx.de/wiki/U-Boot/WebHome

mkmtkhdr:
https://github.com/omnirom/android_device_oppo_r819/tree/android-4.4/mkmtkbootimg (initial source)
https://github.com/osm0sis/mkmtkhdr (patches)

loki_tool:
https://github.com/djrbliss/loki

futility:
https://github.com/jcadduono/platform_external_vboot_reference (initial source)
https://github.com/osm0sis/futility (patches)

boot_signer.jar (requires JRE 8+):
https://forum.xda-developers.com/android/software-hacking/signing-boot-images-android-verified-t3600606

blobpack, blobunpack:
https://github.com/AndroidRoot/BlobTools

dhtbsign:
https://github.com/chiefwigms/degas-mkbootimg/tree/galaxy_tab_a_smt285 (initial source)
https://github.com/osm0sis/dhtbsign (patches)

rkcrc:
https://github.com/rockchip-linux/rkflashtool

sony_dump:
https://forum.xda-developers.com/crossdevice-dev/sony/tool-unpack-format-sony-kernel-image-t3530077

lz4:
https://lz4.github.io/lz4/

magic:
https://www.darwinsys.com/file/

cpio, dd, file, lzop, tail, truncate, xz;
libiconv.2, libintl.8, liblzma.5, liblzo2.2, libmagic.1 (macOS):
https://www.macports.org/

gzip, bzip2, lzop, xz;
awk, basename, bash, cpio, cut, dd, dirname, env, file, find, grep, hexdump, java, printf, rev, sed, stat, sudo, tail, truncate, wc (Linux):
(required system packages/commands)

androidbootimg.magic:
osm0sis @ xda-developers

shell scripts:
osm0sis @ xda-developers (scripting)
Peteragent5, alansj & iridaki @ xda-developers (general method)
SuperR. & tobias.waldvogel @ xda-developers (kernel.elf to boot.img general method)
_that & rayman @ xda-developers (boot.blob general method)
Chainfire @ xda-developers (ChromeOS and SEAndroid general methods)
cybojenix @ xda-developers (Bump general method)
xyz` & k4y0z @ xda-developers (amonet general method)