Compendia is a decentralized network where anyone can create and contribute to open databases of any category (e.g. apps, markets, cryptocurrencies, music, videos, games, etc). Apps and services can pull data from these databases for free.
In the future, Ethereum smart contracts can also use this data (e.g. for DeFi applications).
Think of Compendia as an oracle network, but instead of serving one piece of simple data for one specific topic, the network can serve full data collections from many sources relating to any topic.
You can also think of Compendia as the Wikipedia of databases for apps, services, blockchains, smart contracts, IoT, A.I. and more.