AutoHotkey

AutoHotkey is a free, open source scripting language for Windows that allows users to easily create small to complex scripts for all kinds of tasks such as: form fillers, auto-clicking, macros, etc.

AutoHotkey gives you the freedom to automate any desktop task. It's small, fast and runs out-of-the-box. Best of all, it's free, open source (GNU GPLv2), and beginner-friendly.

Also take a look at Awesome AutoHotkey, A curated list of awesome AutoHotkey libraries, library distributions, scripts, tools and resources.