Hi there, We would like to give our Appian users the ability to sele

From a process model standpoint, you can modify alert settings:
forum.appian.com/.../Alerts_Tab.html

You can also modify the system default email notification settings:
forum.appian.com/.../Configuring_Notifications.html

Thank you, Aleksi, for your timely reply! What you were referring to is to change the alert group from the process developer side, right? The problem is that our people want to select alerts for different event types from their end. Similar to the function that sharepoint has (please see the document attached). Thank you very much!

lins, are you talking about these Notifications?
forum.appian.com/.../Notifications.html

I believe these kind of notifications are only intended for designers and not end users.

so users cannot select from their end and they only receive alert messages if process developer put their names into the process. Am I understanding it right?

I think the closest corollary to the opt-in notification list from SharePoint would be the "Follow" functionality for Records, which allows users to optionally receive News post related to a particular record.

It would also be pretty simple to build your own, more customize-able notification opt in list by :
1) Exposing an action for users to pick the types of notifications they want to receive
2) Set up a process model for each notification type that runs on a schedule and sends out the notifications based on user selection.

The specific details would depend on you specific requirements.