I just remembered some that are also not really dead still, but are firmly in low cap territory since more than 5 years and have some interesting PoW mechanisms:

- Primecoin - was the first coin trying to offer an "useful" PoW algorithm, at least for science (math theory), and allegedly found some "record" prime number rows. Created in 2014 by Sunny King (Peercoin creator), it saw a second hype in 2018 and since then was forgotten. I think also the code was never updated if I remember correctly (see Coingecko).

- Gapcoin - another prime/math based coin, probably created in 2018 (Gecko stats). Heyday seems to have been in 2021, then it ran flat.

- Riecoin - another prime/math based coin from 2014. Like Primecoin, it hyped in 2018 and then never could come close to their previous price, but is now stagnant. (Gecko).

Some of these coins seem to transform from "degenerators" into "low cap oscillators" (See Degenerators and Oscillators), i.e. they have stopped their decline and now are trading approximately at the same price for years. That's perhaps an interesting topic for another thread ...