I built ours with the RFID Jukebox and wrote a little tool called labelmaker to print labels for audio books and music: https://pilabor.com/projects/labelmaker/, but in the end it took too much time to print so many labels :-)
I recently bought the toniebox to hack it for my son's 4th birthday. It has become his favorite object.
I considered building sometime custom, but the tonie hardware is cute, portable, and lovable in a way that would be hard to replicate.
It has been really fun for my wife and I to listen to our favorite music in the car, and then when my son says "I like this song" I "burn" him a little disk that evening.
He's turned into a little DJ, and has memorized a handful of his songs (and dances and sings along).
One caveat is that finding compatible NFC tags is a little bit complicated. if you buy from RFIDfriend [0] then they take a couple weeks to arrive from Germany.
Having just received a toniebox as a gift for my daughter's 1st birthday, this got me so excited. Had no idea this was possible. Gonna get some of the NFC tags next week.
We have Yoto for our kids and I was initially skeptical (the cards are quite expensive) but actually it's been amazing. Probably the biggest benefit that we didn't even know is that they have a sort of radio/podcast thing for kids called Yoto Daily that's really well produced and totally free.
There is https://tonies.com, which is cloud based and pretty expensive, but hackable (https://github.com/toniebox-reverse-engineering/teddycloud).
Then there is the RFID Jukebox: https://github.com/MiczFlor/RPi-Jukebox-RFID
And Tonuino: https://github.com/tonuino/TonUINO-TNG
I built ours with the RFID Jukebox and wrote a little tool called labelmaker to print labels for audio books and music: https://pilabor.com/projects/labelmaker/, but in the end it took too much time to print so many labels :-)