https://bluesyncline.gitlab.io/furby/index.html: 1998 original Furby assembler source code and transcribed to assemble-able code (published in 2018 on github)
furby voices on archive.org

https://cdn.preterhuman.net/texts/engineering/Furby%252C%20Reverse-Engineered.pdf
https://patents.google.com/patent/US6544098B1/en
Furby Autopsy
https://web.archive.org/web/20190725163824/http://www.techdose.com/projects/Furby-Hacking-101/260/page1.html

Furby 2012 has monochrome-LCD eyes and multiple personalities included. It has ultrasound communication “ComAir” for inter-Furby interactions and app connection. It can connect to Furby Party Rockers “mini-furby companions” and later Furby Boom, which is based on 2012-model. Furby Boom can connect to Furblings exclusively and to Furby2012 over ComAir. Party Rockers and Furblings have no moving parts, “holographic / lenticular” style eyes with a backlight LED for illumination. Party rockers have tactile buttons for interaction, Furblings do not react to touch and can be used with Boom only.

2012 teardown on adafruit and its pdf version. Also see another teardown and iFixit

https://poppopret.org/2013/12/18/reverse-engineering-a-furby/
https://habr.com/ru/articles/166377/ and https://github.com/iafan/Hacksby

Furby Connect (2016) has colour-LCD eyes and nRF51822 for Bluetooth connection inside (no ComAir anymore).
FunFact: feature of multiple personalities was scrapped in development. 7 unused personalities are still in NAND (unused audio files). As it has Bluetooth, the FCC was first with disassembling it. See a tear down video on YT.

The app “Furby Connect World” has been discontinued: To Download and use, see https://github.com/Furby-ReConnect/Furby-Connect-World-CDN. For troubleshooting, read this tip.

https://github.com/Furby-ReConnect and https://github.com/Furby-ReConnect/Furby
archived original blog post of Furby-ReConnect

https://www.pentestpartners.com/security-blog/new-furby-teardown/
https://official-furby.fandom.com/wiki/Furby_Connect/Hacking

CCC talk: Don't Feed Them After Midnight: Reverse-Engineering the Furby Connect
Reverse Engineering Furby Connect's Bluetooth Protocol and Update Format and read the docs. There is a beginner friendly fluffd guide
https://furby-science.tumblr.com/post/190181429954/hacking-your-furby-connect-the-quick-and-easy-way
Python tools for handing Furby Connect DLC files
https://pdjstone.github.io/furby-web-bluetooth/ FurBLE - Furby Web Bluetooth Demo
https://github.com/swarley7/furbhax
https://github.com/martinwoodward/pyfluff Python rewrite of Bluefluff

#TODO: describe replacing nRF in Furby Connect

https://github.com/matteoferla/pyfurby
archived replacement-PCB schematics

https://www.instructables.com/Control-a-Furby-with-Arduino-or-other-microcontrol/

Open FURBY (based on Furby BOOM)

Check out modified Furby skins/furs by “The Drunken Witch Co.”, e.g. on TikTok or Instagram

Also search on reddit /r/furby

Furby 2023 on iFixit
CT-Scan of Furby 2023

Hack those Tamagotchis! https://natashenka.ca/

Bitzee flex-PCB actuator LED display toy: discussion on reddit about Bitzee firmware dumping and bitzee disassembly by fcc with schematics too
Watch Carl Bugeja on YT: DIY PCB and flexible actuators 'bitzee-style'