Tired of being locked into systems created by Microsoft or Apple? The following systems are Open Source. Though these have traditionally been thought of as harder to use and "only for experts", this has changed considerably, and many Linux distributions are ready for average users. There are many more than these, but here is a quick sampling.
Sometimes there is basic software that students and faculty need, but the cost can be somewhat prohibitive. However there are many free open source alternatives available, that will suffice (and sometimes are better at certain things than their closed-source commercial alternatives). They will usually run in most major operating systems. Here are a few useful ones.