Back then smartphones were fresh and in the app space there was not as much tracking, rent-seeking, ads, attention economy and cut-throat competition.

Mine pick would be PlantNet [1]. Myself not being an expert in botany it allows me to explore all the plants around me, in the nature reserves and city gardens alike. Works surprisingly well. Obviously the deep learning tech was not as advanced a decade ago, hence I put like the 2010s in the title ;)

[1] https://play.google.com/store/apps/details?id=org.plantnet