As y'all know "Lightning Network" (a.k.a LN) is coming, which allows us to have streaming payment, micro payment, confidential transaction and, most notably, fast & cheap Bitcoin payment fee across multiple coin networks.
LN needs SegWit (or SegWit helps LN to be precise) so we've witnessed a whole bunch of coins beating "SegWit" drum for a while.
(https://bitcointalk.org/index.php?topic=1777136.0)

As few coins start hitting LN drum already, I'll list & update them here for a reference.

On Mainnet

• Groestlcoin   ( Apr. 26, 2017 https://twitter.com/GroestlcoinTeam/status/857157192868397057 ) Thanks to metamorphin
• Syscoin   ( Apr. 27, 2017 https://twitter.com/syscoin/status/857409877609562112 )
• Ripple (https://ripple.com/build/rippleapi/#payment-channel-create, RPID-1224)

On Testnet


In Development

• Litecoin ( https://twitter.com/SatoshiLite/status/858007334471086080 )

Planned

• Decred (Roadmap https://forum.decred.org/threads/2017-decred-roadmap.4937/ )
• Viacoin
• Veltor
• Raiden on Ethereum

⁰ shyliar shared a nice list of LN implementations. (^*I'll update them all here with some research. Thanks!)
¹ Alt bullish market is coming close to its end as of now. Please be adviced before investing your valuable asset in the listed coins.
² Please refrain yourself from promoting a certain coin/asset/whatever unless it is 1) specifically related "Lightning Network" and 2) unfounded in the list above.
  Launch a speculation on the appropriate section, please.