ncd-fe/docs/installing/standalone.md

Standalone Nicolium installation

To install Nicolium in standalone mode, allowing to sign in to any instance implementing Mastodon client API, you only need a static web server to serve the files. As usual on single page applications with client-side routing, the server must be configured to fallback to index.html for non-matching routes.

Example Caddy configuration

nicolium.example.com {
	root * /var/www/nicolium
  encode
	try_files {path} /index.html
	file_server
}

This assumes you're serving Nicolium under the nicolium.example.com domain and the Nicolium files are located in /var/www/nicolium. You can download Nicolium from https://pl.mkljczk.pl/pl-fe.zip or build it from source.