OpenSlot for Outlook - 2026 Pricing, Features, Reviews & Alternatives

OpenSlot answers the question that starts most meeting threads: when is everyone free?

Choose the people and a date range, and OpenSlot reads Microsoft 365 free/busy for all of them, then returns one paste-ready list of every shared opening, written in whatever time zone your recipient reads. In Outlook the list goes straight into the email you are writing. On a message you have received, "Reply with times" opens a reply with your availability already in it. There is also a web app if you would rather work outside Outlook.

What it deliberately does not do is send anyone a link. No booking page, no poll to vote in. The times arrive as plain text in the body of the email, so they survive forwarding, quoting and applicant tracking systems, and the person can answer in one line from a phone.

Privacy is the other half of the design. OpenSlot reads free/busy only: never meeting titles, attendees or message bodies. No calendar data is stored, and availability is computed fresh each time you ask. Access is read-only through Microsoft Graph, and an administrator can review exactly what it asks for before anyone installs it.

Your settings follow you between the add-in and the web app: working hours, minimum slot length, weekends on or off, tentative treated as busy, and the time zone the list is written in. Colleagues outside your organisation are flagged rather than quietly dropped, so you always know what the list is based on.

It works in Outlook on the web, New Outlook, classic Outlook for Windows and Outlook for Mac. Calendars being merged must be on Microsoft 365 or Exchange Online; the people receiving your times need nothing at all.

Free covers you plus one other person across a 7-day window. Every new account starts with 14 days of Pro, no card required. Pro is $7 per user per month or $72 a year and merges up to 40 calendars as far as 60 days ahead. Team starts at $5 per user per month with a five-seat minimum.