Can you list the main types of notifications used by systems to inform users?

Main types of notifications in systems for informing users:

• Push notifications: messages that arrive on the user's device even when the app is not active.
• In-app notifications: messages displayed within the app during its use.
• Email notifications: emails sent to the user's email address with information or alerts.
• SMS notifications: text messages sent to a mobile phone.
• Sound and vibration notifications: used to attract the user's attention.

Each type is chosen depending on the importance of the message and the user's preferences.