Traditional Like system, as you can find on social networks. It uses same reputation system.
Installation of plugin is pretty straightforward. You should add template import to Post Template. For example, you can find post template for Persona Theme under this path: nodebb-theme-persona/templates/partials/topic/post.tpl
Import:
<!-- IMPORT partials/topic/likes_post.tpl -->
Add it wherever you like, but don't forget to delete default one, with chevrons.
By default, it looks like:
Additional list:
