AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
Dapp Store - DappStore is a platform, which lists all popular dApps
SimilarSites - Easily find more sites like those you like.
DappRadar - A list of the best decentralised Ethereum applications
Product Hunt - A website that lets users share and discover new products
AppScope - Appscope, one of the leading directories for Progressive Web Apps (PWAs).