[samtheprogram]

Darwin is still open sourced, but mainly because of drivers and differences in certain other things (threads maybe, Mach ports / IPC, etc) that don’t have the integration or implementation with existing software is a major headwind to attempting a full encompassing Darwin OS.

PureDarwin was (is?) an attempt that hasn’t been able to break through those headwinds.

[spyremeown]

Is Darwin used for something other than research? I'd really love to see some homebrew stuff with this kernel.

[jeroenhd]

There's https://www.puredarwin.org/ which is probably great for partial OSX/iOS emulation efforts. That's it as far as I can tell, though.