Yes there are. Here is one, paper trail. https://github.com/airblade/paper_trail
Its main prupose is to versioning models but I think its also good for your use case since it registers who made each version.
For more gems search at ruby toolbox. Here are the categoties that you should check in this case
https://www.ruby-toolbox.com/categories/Active_Record_User_Stamping
https://www.ruby-toolbox.com/categories/Active_Record_Versioning
Maybe Userstamp is actually better for your use case.