We maintain a list of free VSTs and similar plugins on plugins.audacityteam.org. You can find, test and add plugins to the list.
To do this, you can get access to the plugins space via https://www.audacityteam.org/gitbook-plugins and then edit the relevant sections.
Exact details can be found here: https://plugins.audacityteam.org/contributing/adding-plugins-to-this-site