If you're on United, you can get the aircraft info on their app and match it to the United Fleet website (not affiliated with UA
When you do a flight status search (48 hours prior to departure), you can see what the aircraft type and fleet number is on the status page itself. For example, it has a picture of the aircraft, and above it, it will say "Airbus 320 | #4629". Then you can go to the United Fleet page (just do a Google search for United Fleet), look on the A320 spreadsheet under United Mainline Fleet, find #4629, and it will tell you that the aircraft's registration is N429UA. It will also tell you if the aircraft has winglets, ETOPS, what the configuration is, what IFE system it carries, if it has Channel 9, if it has power outlets, which paint scheme it has (although that's about three aircraft away from being irrelevant), and so on.
There is a way to cheat the system to effectively let you view the flight status 72 hours in advance. Close the app, change the time setting on your device to a time zone in Asia, then relaunch the app.
That's about as much as you can do on UA
, which is more comprehensive than what is publicly available for most airlines. Equipment frequently changes, so that's why it's generally only available and somewhat reliable 48 hours in advance (or technically 72 if you cheat).
Hope that helps!