Hi,
I am trying to find the different events upon which we receive notifications under the Bell icon.

Some of them I have observed so far is
a. When there are Chatter mentions
b. Approval Request notifications
c. Transaction Security notifications

Q1. Are there any other events upon which we might be receiving the notifications? 

Q2. Can we configure custom notifications to be appearing under the bell? For example, change of status field on a cutom object.  We can configure email alerts using Workflows or Process Builder, but I am also looking if I can be notified in Salesforce, for different events.

Appreciate any pointers. Thanks in advance.

- Shiva