What is Open Source?
If you were to go out on the street and ask ten different people what OpenSource software is, you would most likely get ten different answers. The official definition, from The Open Source Initiative, can be found on [Wikipedia|http://en.wikipedia.org/wiki/Open-source_software].
One perspective, from an engineer's standpoint: "Open-source software ... is computer software that is ... provided under a software license that permits users to study, change, and improve the software."
If an engineer is going to rely on a software package for making design decisions that can have significant safety or cost impacts, our engineer needs a mechanism whereby the validity of the algorithms and their implementation can be verified easily. Granted, not all of us are going to go digging around in the code to determine that a particular piece of software actually cranks out viable results; however, the fact that there are a large number of other users who ARE validating and improving the code provides us with a greater sense of confidence than taking some commercial entity's word for it.
There is another peripheral benefit that is often overlooked: the user community can be quite diverse. Through forums and mailing lists, a good deal of support and assistance can be accessed without having to navigate through some corporate "Help" desk. The communities are often comprehensive sources of answers to specific questions.
Cost and Licensing Considerations
Note that there's nothing in the definition of OpenSource software about its cost. Fortunately, many of the OpenSource solutions now available for engineering applications also happen to be free of any licensing fees (although this is not always the case). Some of the OpenSource software that is available for free is restricted to personal-use; you are not allowed to use it in your commercial engineering practice. Yet many of the best tools we have encountered are not hindered by restrictive licenses. Still, one must be aware of such restrictions to avoid ethical violations or possible legal problems.
One's focus will naturally be upon Free and Open software. But, this particular category may not provide a viable solution for every circumstance. Therefore, as necessity dictates, the engineer should swerve off the path to explore some possibilities that are not free, or that may involve restrictive licenses. The goal is to identify the most cost-effective tools for engineering applications. And, of course, part of the cost that must be considered is the time one must invest in learning how to use the software. It lies in the engineer's purview to understand the software and make informed decisions about which kind of tool to use.