iPodWizard is a Windows-only custom firmware manager for the iPod Video and earlier. It is abandonware, but is still the most popular firmware manager for iPods. It has the ability to add and edit Apple's stock firmware.

iPod Wizard
Ipodwizard.png
Logo for iPod Wizard
DeveloperTheWizard

Screenshots

(Any Windows users please consider adding screenshots, thank you)

Resources

Archive.org download of iPodWizard Version 1.3: https://archive.org/details/iPodWizard
A collection of themes for iPodWizard (from archive.org): https://archive.org/details/ipodfw