[x] Otterscan - MIT-licensed, alpha, maintained, TS. Very slick and simple, uses ethers.js to talk directly to a node. But probably too simplistic for our needs.
[x] EthVM - SSPL license, JS/Vue, maintained. Relies on Apollo graphql backend that's not available.
[x] Blockscout - GPL license, popular, mature, maintained, Elixir. Solid, but elixir code is unreadable, unmodifyable, unmaintainable.
[x] Ethernal - BSL, maintained, JS. Docs for self-hosting aren't very good; API backend doesn't appear to be available.
As an alternative/backup to our existing explorer.
Candidates: