For our servers and development workstations we regularly use Linux (preferably Debian distribution); look at arguments for Linux.
With Linux/UNIX we develop with the scripting and programming languages C, C++, Tcl/Tk, SQL/MySQL, Perl, Prolog, UNIX Shell (bash, zsh, POSIX-sh), HTML/PHP, Java and Fortran.
Besides for Linux we also develop software for Win32, SunOS and OpenVMS as target platforms on our own development workstations, including porting from/to these.
On our Linux servers we use Apache/PHP, BIND, ClamAV, Courier-IMAP, CUPS, MySQL, netfilter, NIS, Postfix, ProFTPD, Rsync, Samba, SqWebMail, SSH and VNC, among others.
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