Apps can register to handle URIs, which can be local, or something like http://*.reddit.com/* http://*.reddit.com/* so whenever a link to reddit is found in say

Apps can register to handle URIs, which can be local, or something like http://*.reddit.com/* http://*.reddit.com/* so whenever a link to reddit is found in say an email or web page, you can choose how to handle it, either via the browser app, or a reddit client.