This is the original Lunetius! Some comments from its lovely maker (with minor edits for the showcase format):
Lunetius the lacerna is a cloak, where I could not quite figure out the history, but seems to have been used for both civilian/representative and military purposes. There is a text passage where an emperor (Domitian, early empire) apparently complained about people parading around in their colourful lacernae when going to the theatre, and passed a law that only allows white ones 🤷
It's essentially also a rectangle with rounded corners, that is closed by a fibula - a clasp/brooch/pin - over the right shoulder. It can be worn almost closed or whipped back around the shoulders (and you can still draw your sword easily even when it's closed), it doesn't provide as much protection against wind or rain though, but it's still better than just a tunica or even a toga.