Since you asked: nano is the only _pure_ cryptocurrency using a variant of PoS called Open Representative Voting. Other projects are piling on features to chase trends (defi, smart contracts). The inherent problem with having multiple functions, is that it inevitably takes away from the primary purpose of pure store and transfer of value. Cash for example, can only be cash and has no utility except that of being stored, or switched for a good or service, or another form of cash from another country. If cash suddenly had a "feature" (such as fees, rewards, etc), the feature in itself will suddenly take priority over cash's original purpose of being a means of exchange and store of value. Transfer and store of value can't be separated. In order for something to be a good store of value, it needs to be a good transfer of value.

Taken from a Q&A with nano's creator[1] around a question of why doesn't nano implement smart contracts:

> Smart contracts can’t cause side effects to happen. They can’t move property and they can’t negotiate unforeseen disputes. When you carefully look at it, all smart contracts take the form of a prepayment and slow release of locked-up funds. People haven’t and won’t use this for multiple reasons. Economically the opportunity cost of locked-up funds means they can’t be used elsewhere while locked up. From a practical standpoint, something simple like a rental smart contract could mean you’d have to lock up your year’s rent to slowly trickle out to your landlord. People simply don’t have this much money to lock up. Smart contracts can’t sample unforeseen circumstances, something like a judge ruling in contradiction to a smart contract means it will continue to operate incorrectly given the new situation. Oracles in smart contracts will very quickly become infeasible. Consider writing a contract about a building in a remote town, who is the person that’s going to go on location, make the determination, and feed the input into the system? How are we sure they aren’t coerced to lie?

[1] https://changenow-io.medium.com/ama-with-nanos-founder-colin...

Ethereum currently has a working proof-of-stake network. As far as I know it's the most scalable version currently live, capable of millions of nodes without any sort of delegation. Right now it has over 100,000 nodes and has run perfectly since it launched on Dec. 1.

However, so far it doesn't have users other than the stakers themselves. It's not all that hard to transition everything over, it's just that it's a live $200 billion economy and they're being really careful about it. Should happen next year though.

Tezos is interesting, upgrades happen without forks and are voted on-the-chain. It’s developer-friendly and seeing slow adoption with some governments. Allegedly France’s C3N uses it and Reno is testing it with NFTs.

Bonus points for it being overseen by a Swiss non-profit, they fund development efforts and encourage adoption.

Who knows what the end result it, but I think the ideas there make it favorable compared to BTC and ETH. Not to mention lower transaction fees :).

Cardano and Polkadot iirc.

NEO, Dash, QTUM, Algorand

Algorand

Nano