Appian vs. Power Apps

IMHO, Power Apps is made to replace MS Office scripting and other kinds of shadow IT and pull things into Azure cloud. But its purpose is not the implementation of complex business processes.

Appian is designed from the ground up to excel in such complex business process scenarios.

I agree with stephan about Power Apps... in your case , it depends on the project you would like to implement.

IMO PowerApps is closer to no code than low code and is less flexible. If you want more flexibility, you need to switch to high/pro code. I think Appian is somewhere in the middle, a little more complex but more flexible with what you can do whilst still remaining low code.

Also agree with Stefan, targeted towards more niche/targeted apps for a subset of users. Appian is better at enterprise that orchestrate processes across the organisation.