Closed source software, specifically Microsoft software, offers a confusing myriad of licensing options. Microsoft license options include:
Full Retail Licenses – Transferable license for software.
Upgrade Retail License – Nontransferable license for software which insures the existence of other qualifying products.
OEM License – Non transferable, even to other hardware which you own.
There are also volume licensing programs like Open Licensing, Select Licensing, Enterprise Licensing, and Enterprise Subscription Licensing. These are targeted at different size companies, and you need to read the details to see which is best for your organization.
There are other special licensing programs like MSDN Subscriptions, and Academic Licensing. These licenses let you build software, but when you put your software into production, you have to buy “real” licenses for the software upon which your solution depends.
A good overview can be found here. You can even pay people to help you figure out the best licensing to choose.
In addition, there’s something called Software Assurance, which is essentially a subscription program which grants you free upgrades.
There are also a batch of licensing programs available to Microsoft partners.
If it seems confusing, it is. You can invest substantial time and research into figuring out which licensing program makes the most sense for your company. If you don’t invest the time, you might end up paying extra for the same software. Some of the licensing programs are also a bit of a gamble. You might sign up for Software Assurance because you want “free” access to something like Longhorn Server. However, if the product slips, you might have paid for a subscription which didn’t get anything out of.
With free open source, there’s none of this. You just download the software and go. The only terms you typically need to consider are the redistribution rights.