I suspect nobody round here but me is using the Haiku OS (yet!), but I should let folks know anyway that I've ported Csound 5 to that platform.
It's a fairly complete, though command-line-only, port of 5.17.6. (Sorry it's not 5.18, but there were a number of delays, including a drive crash...) It includes real-time audio out and MIDI in, but no audio-in or MIDI-out as yet. None of the FLTK widgets are available, as that kit has not been ported to Haiku.
For reference, the package is at:
The source changes have been mailed to jpff and hopefully will get merged with the trunk.