Filename            | Description
--------------------|----------------------------------------------------------------------------------------------------------------------------
banlist.dat         | stores the IPs/Subnets of banned nodes
agrarian.conf           | contains configuration settings for agrariand or agrarian-qt
agrariand.pid           | stores the process id of agrariand while running
blocks/blk000??.dat | block data (custom, 128 MiB per file); since 0.8.0
blocks/rev000??.dat | block undo data (custom); since 0.8.0 (format changed since pre-0.8)
blocks/index/*      | block index (LevelDB); since 0.8.0
chainstate/*        | blockchain state database (LevelDB); since 0.8.0
database/*          | BDB database environment; only used for wallet since 0.8.0; moved to wallets/ directory on new installs since 0.16.0
db.log              | wallet database log file; moved to wallets/ directory on new installs since 0.16.0
debug.log           | contains debug information and general logging generated by agrariand or agrarian-qt
fee_estimates.dat   | stores statistics used to estimate minimum transaction fees and priorities required for confirmation; since 0.10.0
budget.dat          | stores data for budget objects
masternode.conf     | contains configuration settings for remote masternodes
mncache.dat         | stores data for masternode list
mnpayments.dat      | stores data for masternode payments
peers.dat           | peer IP address database (custom format); since 0.7.0
wallet.dat          | personal wallet (BDB) with keys and transactions; moved to wallets/ directory on new installs since 0.16.0
.cookie             | session RPC authentication cookie (written at start when cookie authentication is used, deleted on shutdown): since 0.12.0
onion_private_key   | cached Tor hidden service private key for `-listenonion`: since 0.12.0