Flarum is a free, open-source, and next-generation forum application that helps you to build your online discussion forum. Flarum looks and feels great out of the box. The user interface is streamlined so you can spend less time clicking and more time talking. 

For installation steps, click on the link 

https://wiki.crowncloud.net/?How_to_Install_Flarum_on_Ubuntu_20_04