What are all the payment channels implementations? I know the Lightning Network (which Electrum wallet experimentally supports) is an implementation of a payment channel, but Mastering Bitcoin (2nd ed.) ch. 12, § &quot;Routed Payment Channels (Lightning Network)&quot; says:

The Lightning Network was first described by Joseph Poon and Thadeus Dryja in February 2015, building on the concept of payment channels as proposed and elaborated upon by many others.

What are the &quot;many others&quot;? Is the Elements Project's &quot;pegged sidechains&quot; &quot;building on the concept of payment channels&quot; too?
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.