Teensy has a nice audio library if you're interested in real-time sound synthesis and stuff like that, as well as MIDI-over-USB support. Along with a fast processor and a tiny footprint, it's pretty useful for making musical instruments.
I don't know about Eurorack stuff, but yes, for analog audio output, Teensy sells an audio adapter board with line-level output and a headphone jack [1] and that's what I'm using. The audio data is sent digitally using I2S. The audio library also supports cruder ways to do DAC yourself if you don't need it to be as high quality.
It would be nice if there was a Teensy board with analog audio output, though.
Depends on how you mean. My modular synth has many Chord Organ and Radio Music modules, by Tom Whitwell of Music Thing Modular. They're all Teensy 3.1 and the audio's taken off an extra pin (not in the DIP configuration, and I've forgotten to include it before) and buffered with simple TL07* op amps. It's mono, I think it's 44.1k and effectively 12-bit, and I suspect it needs the op-amps for buffering and boosting, but it's absolutely there and that's the 'cruder ways' and though it's primitive and mono it absolutely works, and works surprisingly well with filtering/reverb/etc.
What I'd like is a Teensy board with SERIOUS analog output that still works with my Chord Organ firmware. Like 192k (or indeed 96k) and 24 bit… but I could get a lot of use out of even low-bit at elevated sample rates, because one of my options for coding stuff on the firmware and Tom's eurorack module hardware is using the Teensy's library to produce multiple square waves.
If I'm outputting square waves I can use almost arbitrarily low-bit word length, but high sample rate will greatly reduce aliasing, and not just for high frequencies. The Teensy raw audio stuff has a characteristic grunginess on squares and saws that is mostly or entirely about aliasing.
Teensy audio adapter has SGTL5000[1] running on the board and in my opinion it is highly customizable. It provides up to 96KHz sample rate (44.1 KHz with teensy's clock I guess) with 16bit sample size for ADC and DAC so I don't think it's low quality.
