Repository: https://github.com/jetmonk/cl-libserialport
Dependencies: babel, cffi
Sigrok C-library home page: https://sigrok.org/wiki/Libserialport
It allows listing of available serial ports, opening ports, blocking and non-blocking IO, and has an event listner. It's nice because the sigrok folks have done the tricky cross-platform stuff.
License: MIT
protocol system programming