In a few newbie words - AppLink is a webpage full of meta headers. These meta headers redirect the client to appropriate application or store on their device.
E.g. if you create an AppLink page for MyXYZapp
, which is an app for both iOS and Android, than probably you'll have a pseudo code in your AppLink page header like this:
//client is visiting the applink:
if the client is on Android:
try:
open app with bundle id `com.AndroidCompany.MyXYZapp`
else if MyXYZapp is not present on the device:
redirect client to Play Store page of MyXYZapp
else if the client is iOS:
try:
open `com.iOSCompany.MyXYZapp`
else:
redirect to AppStore page of MyXYZapp
else if client is visiting from any other OS:
redirect to AppStore / PlayStore via browser (or create your own behaviour)
EDIT:
Facebook itself now provides applinks, as described here:
https://developers.facebook.com/docs/applinks/index-api/
EDIT, THIS NO LONGER WORKS:
Now most people do not own servers to host these kinds of pages so facebook offers free hosting and very easy tool to generate AppLinks for your apps:
https://developers.facebook.com/quickstarts/?platform=app-links-host
read more here:
https://developers.facebook.com/docs/applinks/hosting-api
p.s. hope the URLs don't decay and dissolve through the coming centuries
p.p.s the URLs have decayed under 2 years. Crazy