A small list of Kindle extensions I have found interesting or useful. Not all of them work on either soft-float (<= 5.16.2.1.1) or hard-float (>= 5.16.3) firmware. If you want to discover more extensions go explore the Kindle Developer’s Corner section on MobileReads.
Make sure to read the latest patches/updates notes for these extensions.
You cannot install these extensions if your Kindle is not jailbroken.
⭐ KOReader: An alternative and feature-complete document viewer, it supports a large variety of formats including EPUB, DjVu, TXT, CBZ and more. It also has custom screensavers, gestures, progress sync, etc. (Hard-float version hasn’t been released officially yet, get it from here instead)
Renametobin/BinaryRenamer: Block automatic updates, ⚠️ make sure you’re only installing one of the two. Works for both firmware types.
⭐ USBNetwork/USBNetwork-lite: Be able to connect to your Kindle via SSH, USBNetwork-lite only works on hard-float firmware and vice versa.
Downgrader: Downgrade to a previous (obviously released) firmware update.
Kindle Bowser Patch: Remove the restriction on what kind of filetypes you can download from the browser (>= 5.16.4).
Gargoyle Interactive Fiction Player Soft-float/Hard-float: A Gargoyle IF interpreter.
Dungeon Crawl Stone Soup: A free and open source roguelike computer game (>= 5.16.3).
Leafpad Text Editor Soft-float/Hard-float: A very simple GTK+ text editor.
Python 2.7 & Python 3.9: The Python programming language for your Kindle script needs (<= 5.16.2.1.1).
ScreenSavers Hack: Customize your Kindle screensavers(needs Python library installed)(<= 5.16.2.1.1) Downloads links found here.
Sox Media Player: Play audio on your Kindle through Bluetooth (<= 5.16.2.1.1?).
Librarian Sync: Build Kindle collections with either a set folder structure or with Calibre tags (needs Python library installed) (<= 5.16.2.1.1).
Doom for Kindle: Play DOOM on old Kindles (<= 5.16.2.1.1?).