- Specs: https://github.com/lightningnetwork/lightning-rfc
- Blogposts on Specs by Rusty Russel (somewhat outdated) https://medium.com/@rusty_lightning/the-bitcoin-lightning-spec-part-1-8-a7720fb1b4da
- Lightning dev mailing list https://lists.linuxfoundation.org/pipermail/lightning-dev/
- Original white paper (Poon & Dryja) https://lightning.network/lightning-network-paper.pdf
- Follow-up by Rusty Russel https://github.com/ElementsProject/lightning/blob/master/doc/deployable-lightning.pdf
- Blockstream - c-lightning (C) https://github.com/ElementsProject/lightning
- Lightning Labs - LND (Go) https://github.com/lightningnetwork/lnd
- Aqinc - Eclair (Scala) https://github.com/ACINQ/eclair Disclaimer: I have personally never used this one.
- Presentation of original white paper (Poon & Dryja) https://www.youtube.com/watch?v=8zVzw912wPo
- Roasbeef: Lightning Network Deep Dive https://www.youtube.com/watch?v=b_szGaaPPFk
- Christian Decker: History of Lightning Network (a bit less technical but I especially like the visualization here and outlook on possible future with eltoo) https://www.youtube.com/watch?v=HauP9F16mUM&list=UU9OcX1kIjsowRRZzl8tD27w&index=12
- Slides from Lightning Concepts Presentation (nice overview) https://teachbitcoin.github.io/lightning_hackday3#/1
- The glossary can be helpful in the beginning: https://en.bitcoin.it/wiki/Lightning_Network
- Good, recent overview of the current issues in LN and how they can be solved: https://blog.theabacus.io/lightning-network-2-0-b878b9bb356e
- Lightning makers (nice, active, implementation-neutral group on Telegram, Slack etc.) https://medium.com/@TheCarter/announcing-lightning-makers-b7fa9ccdfcb5
- LND Slack (other implementations might have similar communities but I don't follow them as closely at the moment) https://dev.lightning.community/
- Collection of Links and Tools (mostly non technical) https://lnroute.com/
- Network explorers
- Mainnet: https://1ml.com/
- Testnet: https://explorer.acinq.co/
- Testnet shops: https://starblocks.acinq.co/, https://testnet.yalls.org/, https://testnet.satoshis.place/
- Testnet faucet: https://faucet.lightning.community/