It's a probate tickler.
I learned about this term from the FamilySearch Wiki, and it was completely a foreign term to me. Here is a definition from the Washington state page:
I learned that ticklers are used in many, if not most areas where probate records are found.
Though there may be some checklists available for examining probate records for our ancestors, I haven't run across one as concise as the current one shown above. Several websites stated they are used to be able to check items off within a time frame. Many are done electronically today.
Perhaps devising a tickler that can be used for searching ancestors' estates would be a benefit. Several of mine run across many months, even many years. This would help me keep track of the process.