The simple, but limited approach:
Add a text field. In field options, set it up to auto-enter the modification account name.
Set up the OnRecordCommit trigger on the layout to perform a script that uses Get ( AccountName ) to create a new record in a related table that links to the current record on your layout. This then builds a list of who modified the record and (if the records in this related table auto-enter a date, time or timestamp), when.