Standard Notes comprises of two main technologies that work together to ensure a private, secure experience. One is the core stack of Standard Notes client applications. On the other end is a simple framework called Standard File used for encrypting data locally and syncing it to the cloud.
If you're interested in using your own private server for use with Standard Notes, you would need to simply self-host a Standard File server. Get started by choosing a path from the menu to the left.
If you'd like to self-host the actual Standard Notes web application, visit the web repo on GitHub.