You can currently query data from Ethereum and xDai. We are already working on expanding our offer to other chains in the future. Furthermore we inject some 3rd party price feeds into our database.
This section aims to guide you in the process of finding the right data tables to work on your project. Different Use Cases of Dune require different data tables to pull data from, study these carefully and you'll recognize what significance each of the data table types has for your Queries and Dashboards.
Most of the tables on Dune are populated by Dune and are just a translation of the blockchain data to SQL tables, but in the case of abstractions and dune_user_generated tables you can actually create your own tables that aggregate or modify the dataset to your need.