There are many programs, but the most obvious are the Berkeley print spooling system and the sendmail mail transfer agent. In addition, there are Berkeley-based operating systems. Some code and many ideas from the BSD systems have been included in Linux as well. For example, there is a standard for the command interpreter or shell. It specifies what the user sees regarding capabilities.
Software developers are then free to develop a shell that offers the specified capabilities.
This included Digital's VMS system and Microsoft's NT, with each of these implemented as an add-on. One final thing that has influenced Linux development is the capabilities of new computer hardware. Therefore, it doesn't have a lot of the baggage UNIX includes. This means that as new technology appears, code can be developed and tested to support the new technology. The downside is that Microsoft works with hardware developers so they will be aware of the hardware before the Linux market is.