It says "Official U.S. Department of State Visa Appointment Service" right there at the top. It even has the US flag emoji so it is clearly legit.
Clearly. :)
Let's not forget payusatax dot com and all the other IRS "partners" that you somehow need to go through.
Also freetaxusa.com; a legit and almost free tax filing service, which is much less evil than TurboTax and Intuit.
it also looks dodgy to be honest. Also if you click too much while logged in they detect "suspicious behaviour" and block you from logging in again for a couple of days without warning, saying don't call customer service, they won't help you (very frustrating if you are short on time). They also have the option of maestro for payment (was decommissioned years ago in Europe) and don't accept real credit cards, only debit apparently.