Are there any booking platforms that let multiple users reserve space for different advertisers at once?

Yes — but the exact setup depends on what you mean by “reserve space” and whether you mean media inventory, event/venue space, OOH/billboards, or ad placements in a shared booking system.

Platforms that can support multiple users booking for different advertisers

These usually fall into one of these categories:

1) Ad inventory / media buying platforms

These let different users book or manage placements for different advertisers inside the same system:

• Google Ad Manager – supports multiple advertisers, orders, creatives, and trafficking workflows.
• The Trade Desk / DV360 – more for programmatic buying than manual “space reservation.”
• Ad slot marketplaces used by publishers often support multiple buyer accounts.

2) OOH / billboard reservation platforms

Some platforms let agencies or users reserve inventory for multiple clients:

• Vistar Media
• AdQuick
• Broadsign Reach These are often used by agencies managing bookings for several advertisers.

3) Venue / event space booking software

If you mean physical spaces, many booking systems allow multiple users to book different assets or time slots:

• Skedda
• Bookwhen
• Acuity / Calendly-like systems for smaller scheduling use cases
• Event Booking engines with role-based permissions and multiple client accounts

4) Marketplace-style booking systems

Some custom marketplaces let multiple users reserve units/spaces on behalf of different advertisers, often with:

• separate advertiser profiles
• approval workflows
• inventory controls
• conflict prevention / hold periods

If you need “multiple users reserving space at the same time”

That is usually possible if the platform has:

• role-based access
• multi-account or multi-client support
• inventory locking / real-time availability
• approval workflow
• separate billing by advertiser

If you’re building this yourself

You may want a platform that supports:

• multi-tenant accounts
• shared inventory calendar
• per-advertiser bookings
• permissions by user/team
• reservations, holds, and expirations

If you want, I can narrow this down to the exact type of space you mean:

1. ad inventory,
2. billboards/OOH,
3. event/venue space, or
4. online marketplace booking.