[Brian]

The built in "Completed" perspective should show you the actions you've marked off today, in a "Completed Today" group at the top of the window.

If you're looking for a way to remove all the items you've completed before today, you could use the "Archive Old Data" feature (under the File menu) for that purpose. Select that menu item, type "today" into the date box, then hit the "Archive" button.

Everything completed before today is copied out of the database, and the "Completed" perspective now shows only those things done today.

Just make sure to always do the archiving on the same Mac. The archive data isn't synced between your devices the way the main database is, so you'll want to keep it all in one place. Hope that helps!