What Ethereum blockchain explorers exist?

Question

What blockchain explorers exist and

1. What special features do they have?
2. Are they open-source?
3. How reliable are they (approximate uptime in %)?
4. Is there a testnet version?

Answer 1

Hosted Main Chain Explorers:

https://ethtools.com/mainnet/chain

Can explore:

1. Contract Addresses
2. Non Contract Addresses
3. Transactions (and their internal steps)
4. Blocks
5. Contract Code

https://www.etherchain.org

Can explore:

1. Contract Addresses
2. Non Contract Addresses
3. Transactions
4. Blocks
5. Contract Code

https://live.ether.camp

Can explore:

1. Contract Addresses
2. Non Contract Addresses
3. Transactions
4. Blocks
5. Contract Code
6. Contract Storage (appears to the be only service to do so)
7. VM execution trace

http://etherscan.io

Can explore:

1. Contract Addresses
2. Non Contract Addresses
3. Transactions
4. Blocks
5. Contract Code

Hosted Testnet (Ropsten) Explorers:

• http://testnet.etherscan.io
• https://ethtools.com/ropsten/chain offline (2010/01/26)
• https://blockexplorer.one/eth/ropsten
• https://teth.bitaps.com/

Hosted Testnet (Rinkeby) Explorers:

• https://rinkeby.etherscan.io

PoA testnet started by the Ethereum team, uses Clique PoA consensus protocol, supported by geth only

Hosted Testnet (Kovan) Explorers:

• https://kovan.etherscan.io

PoA testnet started by the Parity team, supported by parity only

Open source projects:

• https://github.com/gobitfly/etherchain-light
• https://github.com/etherparty/explorer
• https://github.com/maran/ethereum-blockchain-explorer
• https://github.com/blk-io/epirus-free
• https://github.com/ConsenSys/cakeshop

Outdated / defunct explorers:

• https://etherapps.info
• http://ether.fund/explorer