Suppose you have an existing site with ERPNext installed, is it possible to install another app, such as Frappe Gameplan alongside ERPNext on the same site?
Yes you can install multiple apps in single site.
How does that work in terms of what the url directs to? For example, if only ERPNext is installed, url.com will load the ERPNext homepage. So what happens if I install Frappe LMS on the same site with ERPNext? Where does url.com take me?
It would as defined by app.
e.g gameplan is accessbile at site/gameplan helpdesk at site/helpdesk