Calendar Pro
Pick a reminder for any event - from a week before to the start time - and Windows shows a notification when it's due, even if Calendar isn't open. All-day events and milestones remind you at the start of your working day. Part of Calendar Pro.

Double-click an event, or add a new one. With Calendar Pro, the sidebar's Reminders opens a new event at the Reminder field.
Choose a reminder: at start time, 5, 15 or 30 minutes, 1 or 2 hours, a day or a week before.
Calendar schedules the next 31 days of reminders with Windows, and keeps them up to date as you change events.
Windows shows it at the time you picked. Click it to open Calendar - the window you already have comes forward.
Calendar Pro help has every option in detail.
Part of Calendar Pro. Calendar is free. Calendar Pro is a one-off £5.99 upgrade inside the Windows app, bought through the Microsoft Store - no subscription, no account. Try it free for 7 days.
Yes. They're scheduled Windows notifications, so they appear even when Calendar isn't running.
No. Reminders use Windows notifications, so they're in the Windows app's Calendar Pro.
Yes. Calendar Pro has a free 7-day trial in the app, once per PC - no payment details.

Day, Week, Timeline, Month and Agenda - drag to reschedule, week numbers and UK bank holidays.

Tag events by project, filter to one, and log actual hours against planned.

Notes for every day, exported as a formatted site diary for any date range.

Day, week, month and year wall planners in three styles - print or PDF.

Every event for a project, planned against logged hours, with CSV export.

Diary entries, weekly update emails and project summaries - private, on your PC.

Midnight, Graphite, Forest, Plum, Paper and Ocean.

All twelve months at once, with event dots - click a day to open it.

Bank holidays for Scotland, Northern Ireland and Ireland, and the clock changes.

Weekly and monthly timesheets from your hours, and an invoice from them.

Everything in one file - restore with a preview, merge or replace, and undo.
Calendar is free, in your browser and on Windows. Calendar Pro is a one-off £5.99 in the Windows app, with a free 7-day trial.