The Active Directory Replication Status Tool is definitely one that should be installed on all management (RSAT) machines that domain administrators use. It _requires_ .NET 4.0 and .NET 3.5.1 so may not be practical on domain DCs depending on security configurations for them.
- Ask the Directory Services Team: AD Replication Status Tool is Live
- TechNet: Active Directory Replication Status Tool (ADREPLSTATUS) Resources Page (en-us)
- Microsoft Downloads: Active Directory Replication Status Tool
This tool along with the required .NET installer files are definitely required on the Technician's Thumb Drive (Blog Category - check it out as there are lot's of goodies in there).
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book