The UNIX trademark is owned by The Open Group.
For Unix systems that are only talking to other Unix systems NFS (Network File System) is the most popular. If you want to share Unix files with Windows systems, then Samba is one of the most popular ways to accomplish this.
Unix is not very popular with the general public. A more popular version is Linux. Around twenty percent tend to run on this system. Unix has competition also.
The C language has implementations for all popular platforms, including Unix.
Linux
There are a lot of database systems available on unix systems. The most popular "free" databases seem to be MySQL or Postgres and the most popular commercial is Oracle.
LUnix (unofficially, Little Unix) is a Unix-like operating system for the Commodore 64, a popular home computer of the 1980s.
Solaris is a specific version of Unix; the term 'Unix' refers to a classification, and several vendors provide a Unix-like environment. So, in a sense, Unix and Solaris are the same thing.
mainframe computers networking
Yes, Joan is just as popular today, if not more so, as when she was alive.
the most popular operating system multitasking is kernel
Because Linux is actually more popular in most fields these days than certified Unix.