Bitcoin Block Explorers

Explorers provide us with a view of the entire blockchain, enabling us to see the aggregate flow of money and also letting you drill down into specific transactions.

Block Explorers:

bitaps
Bitcoin Explorer
Blockpath Explorer + Addr/Tx Relationships
BlockCypher
Blockstream.info
Blocktime (search by date)
Breadcrumbs (chain analysis)
Know Your Coin Privacy - blockchain explorer + Boltzmann analysis
Mempool.space
Orion (txn visualizer)
OXT (explorer + privacy analysis)
Spiral (strong privacy)
SoChain
Tx Flow - transaction graph explorer
Yogh.io - raw data block explorer

Open Source Block Explorers:

Abe
BTC RPC Explorer
Esplora (by Blockstream)
Insight (by BitPay)
Iquidus
Mempool
Orange
Simple Block Explorer (single PHP file)
Transaction Explorer (Yogh.io)

Other Tools:

BTCParser (wallet monitors)
TX Pusher (conditional txn broadcast)