Hello!

I think you should add AwardFares.com to this list/wiki. Its not an app (yet?) but a web based service to find availability of award fares on Star Alliance airlines. Basic search is free while a premium sub costs $5 a month and lets you do advanced searches and also set up alerts and search further into the future than with the free plan.

Get going by setting an origin airport, maybe a destination and an 'earliest' and 'latest' departure date. Then sort the result on cabin class, number of stops and so on. You can even sort on equipment. For me its the goto search engine to spend my AMEX vouchers.

I would add a screenshot but as a newbie here I'm not yet allowed, sorry.

Disclaimer: I'm not involved other than as an early beta tester back in early 2018.