As of now, Quantum Resistant Ledger (QRL) coin is represented on a few exchanges paired against BTC. Originally being an ERC-20 token, it switched to its own mainnet in 2018. The QRL claims to be the first decentralized cryptocurrency, that is resistant to both classical and quantum computing attacks.
One of the earliest digital coins, Peercoin (PPC) was released in 2012. It was the first to bring the “Proof-of-Stake” concept to life. Peercoin is a peer-to-peer cryptocurrency and is minable. PPC is widely represented on exchanges. You can also buy this coin for fiat currency.