What makes Linux different from traditional Unix GNU Public License (GPL) for the Kernel and OS applications: free to use; get the source; develop and disclose your source. The same Kernel and GNU C libraries (glibc) for different distributions: if you can run an application on one kind of Linux, its a matter of setting libraries to run it on the other distribution. Runs on various computer architectures: x86, SPARC, MAC, IBM, DEC. The fastest developing OS. Various vendor support. Strong community support.