Burstcoin, an underdog that uses Proof of Capacity.
Burstcoin has gone fairly unnoticed for years now. It had smart contracts prior to Ethereum but without DAPP functionality and low marketing never really took off. It's made a recovery in the past 6 months which is great as the coin has quite a bit to offer.
Burst is fast, not RaiBlocks, I mean Nano, fast but it's quick. With the upcoming tangle implementation it will become faster and more in line with IOTA or Nano.
Burst is decentralized and will remain resistant to centralization. The use of HDD over GPU/ASIC mining is that it's harder to centralize. Yes, there are data centers but what's primarily lead to centralization in Bitcoin is low cost, subsidized power. HDDs require far less energy so the difference between expensive power and cheap power becomes low enough that it doesn't matter that much.
Burst apparently wont die. This coin has been around since 2014 and has gone through some rough patches. It's gotten over a lot of it's original issues and has had a pretty strong past year. There was some infighting but the dust as settled and a strong dev team is at the helm. So far they have designed the tangle implementation and resolved a wallet issue that was causing the network to slow down and fork.
Burst allows you to make some money on extra disk space at no extra cost. If those drives were being used anyways you aren't spending anymore power to run them for mining. At time of writing the average payout is around $2 per TB a month - not great but more than nothing . Prior to the Jan/Feb crash payout was around $5/TB.
Burst is probably not on your radar but it is worth checking out. It's actually how I got started in crypto because I was able to setup a miner with an extra HDD I had laying around.
Full Roadmap:
https://www.burst-coin.org/roadmap