Underlight runs best on Windows 7, Vista, or XP. It will play on Windows 8 and 10, but there are some compatibility issues that are still being worked on. The good news is that Underlight has extremely low system requirements. If you have a computer made in the last decade that is running Windows 7, Vista, or XP, it will run Underlight without issue.
The game can be downloaded and installed at https://download.underlight.com/ and is less than 100mb in size, so don’t worry about storage space. Download and give it a try.