CoinSwap looks like what I'm looking for!
For my case further constraints:
- no LN involved, and
- no onchain linkage between the two parties after a swap.
The use case I'm thinking about is a marketplace for swapping mined 'clean' coins for other coins, for a small premium. LN might be cumbersome because of the amounts. CoinSwap seems to be able to solve this. Thx!