I bought one today. It's a "Universal Smartphone Garage Door Controller".
It said "Installs in minutes." In my case, it was about 90 minutes.
It has a wireless hub that took me a while to get connected to the Wi-Fi network. That's not unusual.
It has a sensor that mounts on the door. I suppose this tells the hub whether the door is down or up.
I downloaded the Chamberlain MyQ app from the Google Play Store.
There were a couple of Gotcha's.
I was asked for a code that is printed on the manual. l This was 10 letters and numbers, ending in "03a". It didn't work until I entered it as "03A".
When I ran the app and added the opener, it asked me for the "Brand and model" of the existing opener, but then let me select a manufacturer (Chamberlain in my case) and asked what color buttons I had on the controller. Choices were green, purple, orange, etc. I looked at the control that is normally used in the car and it had black buttons. There was no choice for black buttons, so I chose the first option, green. The app then tried to find the winning combination, but failed. I finally realized that the "Learn" button on the existing opener was purple. As soon as I tried purple, everything worked. The light flashed, the door went up, trumpets played.
So it works, but the hub beeps obnoxiously and a bright light on it flashes for almost ten seconds before anything happens. Maybe it can be disabled, but it seems like their lawyers were overly protective.