Is there any way to play audio off of a TI-84 Plus CE using a program and the built-in port?
I've seen mobileTunes for the I/O port on older models, but nothing for the newer models of TI calculators.

I played music via a steam controller a while back, if that counts.

In theory it would also be possible to play audio using a regular USB audio device, but IIRC at this point usbdrvce doesn't support isochronous transfers which are required for that.

Like commandz said, to properly play audio over USB would require support for isochronous transfers (which are unlikely to be implemented unfortunately - not sure if it's even fully possible because of the lack of interrupt support on the CE).

There was someone in the CE Programming Discord server a couple months back who had hacked together something to play audio over USB without using isochronous transfers: https://github.com/carteeeee/track84

I wasn't able to get it to work myself though so I assume it's a bit finicky.

You can use a program and an Arduino connected to a speaker.

There are two programs for playing MIDIs on the CE which I've had a lot of fun with. MIDI Player CE, by prime17569, plays converted MIDI files on an attached MIDI host, and midiCE, by TIny_Hacker, lets you use your calc's keypad as a MIDI keyboard. Both require a MIDI host; my best experiences have come from SpessaSynth.

Sorry to necropost, but you can also play synth frequency ranges with a TI Hub Innovator, which just connects with a micro usb cable.

1) 2 days is not a necro
2) I am surprised genisis didn't say 'oh, this'll be a feature of kodeykode OS Evo"
3) I feel someone could also make a moibleTunes CE seeing that there is already a converter. It would be compatible with the same appvar songs.