Changes appear for everyone with the budget open as they are made. The budget bar shows who else is there, and a line shows who is on it.
Each cell remembers who changed it last; hover it to see. A line's details say who last changed it and when.
If two people change the same cell at once, the first one saved wins and the other person is told, with their value, so they can type it again. Nothing is silently overwritten.
Not what you were looking for? Write to hello@actualsbudget.com.