Sikuli

The good:

• Sikuli can do anything that a user can do on a computer from the mouse, keyboard and monitor.
• It's OS agnostic. (Java!)
• It has a built in IDE that's reasonably easy to use.
• The syntax is very simple (Python!)
• You have the full power of Jython . . . which essentially means you have all of Python and all of Java working for you
• It has the ability to match images on the screen. (This is really the core of the program, and it works very well.)
• You can adjust how exactly it matches the images on the screen. (Default is 70% match, but you can go as high as a 99% match.)

The bad:

• The IDE isn't fast. (It's a Java program, so this isn't really a surprise)
• It's not entirely obvious how to work with Sikuli from a different IDE. (There are examples for some of the more popular ones, but not for Atom, VIM, or VS Code.) Most of the code is very simple, but saving from another IDE can mess up the screenshots.
• Sikuli sometimes recognizes a "match" for an image on the screen that is incorrect. (This can be adjusted to correct for this, but can result in unexpected behavior)

The Ugly:

• The IDE will sometimes freeze for long periods of time. (5+ minutes) I typically just shut it down and restart it when that happens. Frequent saves are a must!

Verdict:
Sikuli is a long way from perfect, but it's better than anything else that will work on non-windows computers.

Any task you can do on a computer can be scripted with Sikuli and thus automated. Awesome!

I use it all the time in my computer breaks to do automated tasks.

Tip:
If you need more flexibility you can do an application with winforms, java, etc and trigger its GUI buttons with sikuli. In that way you have the power of sikuli and the power of that other programing language. Thus you can automate more things and faster.

Free, open source, simple to use.