What are the key Journey Builder activities available within a journey?

Wait activities:
— Wait by Duration: Pauses for a fixed time period (hours/days/weeks).
— Wait Until Date: Pauses until a specific date/time field on the contact record.
Decision activities:
— Decision Split: Routes contacts down different paths based on data attribute conditions (up to 10 paths + default).
— Engagement Split: Routes based on whether a contact opened or clicked a previous email in the journey.
Einstein activities:
— Einstein Send Time Optimisation (STO): Delays each contact's email send to their individually predicted optimal send time within a window.
— Einstein Engagement Frequency: Suppresses contacts who are predicted to be over-messaged.
Other activities: Email send, SMS, Push Notification, Update Contact, Sales/Service Cloud Activity, Advertising Audience, Custom Split (via API activity).