An example would be a productivity app that only has a flip switch for High or Low productivity. Whenever you need to be extra productive, just open the app and set it to High.
Some users were utterly convinced that their machine was running faster than ever before, when in reality the malware did nothing other than begging for cash payments. Often the opposite by slowing down the machine with continuous pop-up advertisements and other nasties.
Placebo apps that make your Internet faster are as old as the Internet itself though. I am guilty. In my defense, that was 20 years ago.
The fact that placebos are effective is precisely /because/ they're effectively tricking whatever badly-understood connection there is between our thinking and our body. I imagine that there are degrees to this: 'tricking' ourselves to be productive by deciding to clean our house instead would generally not be called a placebo, whereas taking a sugar pill that lifts us out of depression probably would.
But fundamentally they're just the same thing on a spectrum: an improvement as a result of something that we /know/ should not be effective by understood, biological pathways.
Would work at what? Make people 'happy'?