Kudos to Dc5e for KindleComicParser!
Since I'm on a Mac, the script is nearly useless without a VM, so I came out with a python script that's almost identical but more portable for *NIX systems.
I additionally bundled the whole workflow (HTML/NCX/OPF generation, kindlegen, kindlestrip) in an AppleScript droplet for MacOS users.
You can find the standalone script along with the droplet at https://github.com/ciromattia/kcc
I plan to add support for CBR/CBZ opening to the droplet very soon (comic2ebook.py already has), and extend the workflow with some image manipulation (margin removal, contrast, resizing).
Hope you like it