It was ok. Back when I ran BeOS as my primary OS (2001 or so) I built half a C++ web application on BeOS, the other half on a HP-UX server logged in through an X terminal using ftp to sync between the two. Not much support in the wider *nix ecosystem though, so anything big would often fail to build.
I regretted having to move away from BeOS, it was by far the most pleasant OS I’ve used, but the lack of hardware and software support killed it.
In college I wrote a web server in beos and ported it back to Linux, learning pthreads along the way. Bonus achievement was making it multithreaded, so I got that for free, since beos makes you think architecturally as multithreaded first
Surely it had a cli, UNIX like directory navigation and a couple of UNIX command like utilities.
But good luck porting UNIX CLI software expecting a full POSIX environment.
If I am not mistaken, Haiku has done most of the work regarding POSIX support.