Is anyone building a Lightning-like network on Ethereum, offering cheap microtransactions and secure 0-confs?
Heiko Hees has presented such project at the DEVCON1 conference: https://www.youtube.com/watch?v=h791zjvf3uQ
It is called Raiden. According to Heiko, it is implementable with the current capabilities of Ethereum network, unlike Lightning or Duplex Micropayment Channels, which both require some changes in the Bitcoin (even if simply fixing transaction malleability issues).
Here is the Raiden's github: https://github.com/heikoheiko/raiden
hot off the press: http://etherapis.io Micropayment platform for generic API calls built on ethereum.
Also see SWAP https://github.com/ethersphere/swarm/wiki/Swap which is a specification for generic micropayment scheme suited for pairwise accounting between peers. Its go implementation using ethereum is used for accounting in the swarm decentralised content distribution and storage platform.
Both by the ethereum go team
The Go Ethereum Swarm guys are working on SWAP, a micro payment channels for the SWARM protocol.
Peter and myself have been working on Etherapis (see Viktor's comment), a Gohergala (a golang code competition).
Another example is my whisper-payment-channel. While the other answers either require a separate executable or client this example requires no modification to go-ethereum and requires no additional software other than an Ethereum node supporting Whisper.