Unix is the Operating System of choice to run on workstations. Workstations are machines generally more powerful than PC's and Macs but this is changing fast as PC's get stronger and faster. Some workstations in existance today are Suns, SGI's, DEC's, HP's, and IBM's.
Not all workstations are compatable as they run different versions of unix that tend to be proprietary. Because of this, software compiled and run on one system will most likely not run on a different system (ie. software for a Sun will not run on a HP system). But when these systems communicate over the Internet via TCP/IP protocal, they can all talk to each other. You can also get shareware software unix operating systems such as FreeBSD, NetBSD and Linux that might run on the proprietary hardware made by the before mentioned companies.
Application software, such as browsers and editors can be compiled to run on any computer. A good source of this in shareware is GNU Software that is produced by the Free Software Foundation. Some of the best software is free... such as Apache, the web server most used on the Internet. It is maintained by programmers and hackers all over the world and is available for free with source code (so you can make changes that you like).
Unix Tools exist all over the net and you can find commercial as well as shareware software to use.