Today I spotted a rental with the text AWTO in catchy light blue on the side, and I looked it up on google. I found out it is a car sharing - the first I know we've had in Buenos Aires.
You need a DNI and a local DL to be able to use it.
Just download the Awto app (available for both Android and iOS) or visit https://awto.com.ar/, fill in your details, take a picture of the front and back of both your DNI and DL, take a selfie holding your DNI to validate your identity.
Once your account has been set up, you can pick either a compact vehicle, a premium vehicle or a cargo vehicle. There are per-minute fees both driving and parking, and a flat daily fee (from $3000 upward, i.e. 40 USD at the current blue rate).
You will need the app to unlock the car, so even if you can reserve your vehicle from your computer, make sure you've downloaded the app.
You can pay as you go with Mercadopago (using a card) or pre-pay with PayPal.