Teammates' changes appear as they save. When several people work in the same deck, each person's changes show up in everyone else's deck within a moment of being saved, with no refresh. Two people can work on the same slide, and even on the same widget, and both changes are kept. Only when two people change the same thing at the same moment does the later change win.
Undo is your own. Ctrl+Z (Cmd+Z on a Mac) undoes only your own edits, never a change a teammate made in the meantime, and your undo history stays intact when their changes arrive.
See where teammates are working. When a teammate has a widget selected, you see a thin outline in their colour around it, with their name, and the slide list shows whose initials are on each slide. There are no moving cursors. For a deck, the Team Access panel has a switch, Show where teammates are editing. Only the deck's managers can change it.
What a teammate is working on stays theirs. If a teammate is already typing in a text box or a text flow, a double-click tells you who it is and leaves that box to them until they have finished. A widget a teammate has selected is theirs while they are working on it: clicking it tells you who has it and leaves your own selection as it was, and selecting several widgets at once, by dragging a box around them, Select all or Select similar, picks up the rest and tells you how many were left out and who has them. The widget frees up as soon as they select something else, close the deck or move to another browser tab, or after about a minute without a click or key press from them. Only selections of up to three widgets are held this way, so a large selection never holds up anyone else. All of this works while Show where teammates are editing is on.
Shortcuts that behave as expected. Ctrl+X (Cmd+X) cuts selected widgets. Ctrl+Shift+Z redoes on Windows as well as Ctrl+Y, and shortcuts keep working with Caps Lock on. Ctrl+S (Cmd+S) saves straight away and confirms it, instead of opening the browser's save dialog.