This question isn't gamedev per se but it is definitely relevant. Still, if it's off-topic, please direct me to the proper SE page.
This question has probably already come up many times but I'd like to take a complete approach here and also up-to-date (whatever I may find online might be from 1/5/10 years ago and so isn't of much value to me).
So - is DirectX free for commercial use? What do I mean by that? Is it free to download DirectX SDK (or whatever it's called nowadays) and develop my game? Are there any fees involved in publishing and selling my game if it uses DirectX? And in the spirit of covering it all - using DirectX implies using Windows (which isn't free) and maybe Visual Studio? To that last one - is it absolutely necessary to use VS? Also, is it practical to use any other IDE? And are there any other (implied) costs like that "using Windows" one?
My friend sent me this EULA snippet saying that it's only free if I'm the only user of the software I develop so this must mean I have to pay for DX for commercial use.
SOFTWARE PRODUCT. You may install and use the SOFTWARE PRODUCT on an unlimited number of computers, including workstations, terminals or other digital electronic devices ("COMPUTERS") to design, develop, and test software application products for use with Microsoft operating system products including Windows NT Workstation 4.0, Windows NT Server 4.0, Windows 95 and subsequent releases thereto ("Application"). You may install copies of the SOFTWARE PRODUCT on up to ten (10) COMPUTERS provided that you are the only individual using the SOFTWARE PRODUCT on each such COMPUTER.