How to use another Front end framework such as Bulma in sage instead of Bootstrap?

I just want to try Bulma with Sage. Is that possible?

Bulma is already an option when installing Sage 9 with composer.

composer create-project roots/sage your-theme-name dev-master

I want it to be installed in Sage8! Is that possible?

You can install Bulma on Sage 8 using Bower via bower install bulma. You can read more on theme development & building at the docs here.