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Yes: Rootstock ( https://www.rsk.co/ ). This exists as a sidechain to the bitcoin network and implements the Ethereum virtual machine. It launched on mainnet yesterday.

s/mainnet/testnet/ according to https://media.rsk.co/announcement-upcoming-rsk-testnet-reset...

No, it's currently running on mainnet: https://media.rsk.co/getting-started-with-bamboo-rsk-mainnet...

Keep in mind that rootstock currently is a federated sidechain, so it is decentralized only insofar as you consider federated cryptocurrency systems to be "decentralized" (and different folks disagree about this)

eos.io just released alpha ahead of schedule https://steemit.com/eos/@eosio/eos-io-dawn-2-0-released-and-...

Quite a few:

https://www.reddit.com/r/ethtrader/comments/6b64if/list_of_e...

If Tezos ever arrives it might be a viable alternative for certain use cases.

Look at Tezos Github commits: https://github.com/tezos/

Most of them are shallow changes or "busy work" to show activity. I have been watching FileCoin and Tezos Github, and I wouldn't expect much from either one of them.

NEO, Stratas, NXT and QTUM are the ones I've been following.