Although Megaventory does not natively support email or popup notifications, there are two methods to get notified for the low stock products:
One can create a List View under the Inventory screen with the 'Show only products which need to be ordered' checked:
This can be done for specific locations and/or for specific suppliers and that way one can create multiple such List Views.
That way the List Views will show non-0 quantity whenever your On-Hand availability is below the Alert Level that has been set.
The non-0 quantities in these List Views will display the low stock products which one can display and make purchases as necessary. The regular checks can be once per week or once per day (depending on the volume of your transactions) or simply after a sale has been fulfilled and stock may have fallen below the alert level.
A low stock Zapier trigger can be set-up per product via Zapier (www.zapier.com). Then, the Zapier action can be anything (email, SMS, Viber, Whatsapp, etc). For more, refer to the Zapier section in the documentation.