This plugin lets you format Discourse posts with Sᴍᴀʟʟ Cᴀᴘs.
Follow Install a Plugin
how-to from the official Discourse Meta, using git clone https://github.com/DawnPaladin/discourse-small-caps.git as the plugin command.
You'll find an "Aᴀ" button in the post editing toolbar; click it to add [smallcaps] tags around your text.
If you have issues or suggestions for the plugin, please bring them up on Discourse Meta.