A calendar, and appointments on it
One calendar of everything with a date — appointments, milestone due dates, invoice due dates, proposal expirations — and appointments you create for visits, estimates and meetings.
Everything with a date is on one calendar: the site visit you booked, the milestone due Friday, the invoice due next week, the proposal that expires at the end of the month. Jobs stay the record; the calendar reflects them, so a moved milestone moves on the calendar by itself.
Appointments are the dates you create — a visit, an estimate, a meeting — with a client and a job attached if there is one, and a warning when two overlap. Email digests of your day and your week are a Professional feature.