A tool that you might not think would be used for video games would be PowerPoint, yet when you look at some its features it quickly shows why it can be. Although you might not be able to create some lavish assets like most other programs, one thing you can make easily are the GUI files.
The Smart Shapes that come built within PowerPoint allows you to create, combine, and remove and assortment of random shapes together. The tool is incredibly powerful and can save you a lot of time if you want to create some quick and easy assets for your game.
I regularly use PowerPoint when I want a GUI component within my game just because of how fast and easy it is to use it. I can open it up, put the file together and then export it out as a PNG file to the folder I need.
The Smart Shapes isn't the only thing that makes it valuable, the 3D and texturing options is what really makes it shine. So if you want to make a button and want to give it the appearance that it curves out or in and adjust the lighting to make it appear like it is coming from one specific direction, all of that is available within PowerPoint. Need to add a texture and want it to tile? Want to control the scale of the texture? want to change the material and its lighting effects? Yup, all capable within PowerPoint!
Whether you want so custom gradients, 3D effects, transparency, or just about anything you can think of, you are able to do it in PowerPoint. All you need to do is select the item you created and save as a PNG file the folder you want.
Another added bonus is the vector-like scaling that can be done. The object in PowerPoint will keep its quality whether you scale it up or down, but when you export it out of PowerPoint it will reflect the image quality in which you saved it as. so if you have a 3.5" image and save it out, it will have roughly a 512 x 512 image size. If you doubled the image in PowerPoint before saving, you would get 1024 x 1024 for a size and have a better looking image. The quality and size all depends on what style of game you are making and the exporting doesn't always work perfectly in which you will need to open and edit the file in something like GIMP.