User events in Craft 3
There aren't specific User element save events in Craft 3, but you can listen to EVENT_AFTER_SAVE_ELEMENT and check if the element is a user like so:

Event::on(\craft\services\Elements::class, \craft\services\Elements::EVENT_AFTER_SAVE_ELEMENT, function(Event $event) {
    if ($event-&gt;element instanceof \craft\elements\User) {
        // Do your thing.
    }
});


For user activation, there's EVENT_AFTER_VERIFY_EMAIL:

Event::on(\craft\services\Users::class, \craft\services\Users::EVENT_AFTER_VERIFY_EMAIL, function(UserEvent $event) {
    $user = $event-&gt;user
});