What are all the payment channels implementations?
The Lightning Network is much more than an implementation of a payment channel. It is a peer-to-peer network whose core purpose is to route payment through a set of multiple payment channels.
Then, i think you are confused with regard to the quote: &quot;many others&quot; here refers to
persons not projects. See this wiki page for mentions of some of them.
Finally, as you mention Elements is defining sidechains (a peer-to-peer network whose core purpose is to update a block chain that is somehow pegged to Bitcoin) which are not &quot;building on the concept of payment channels&quot;.
However, payment channels may (not yet deployed) be a good abstraction for interconnecting sidechains with Bitcoin or in-between them.