Lightning torch, El Salvador( Bitcoin Beach Wallet, Chivo).

Blockstream offered stickers over lightning at the start when people were figuring it out

Going through the implementations and the teams behind them could be fun. (Eclair, LND, CLN) Or the lesser known implementations (electrum, immortan) and further on with LDK

Establishment of standards (BOLT11/12, LNURL/Lightning Address, dual-funded channels) 🤔