Kraken is one of the biggest crypto exchange, founded in 2011 and the largest bitcoin exchange in volume. You can stake around 10 crypto currencies "On-Chain" and especially Kusama and Kava.
What coins can you stake on Kraken?
Democratic Republic of the Congo, Republic of the Congo, Lybia, Afghanistan, Iran, Irak, North Korea, Syria, Tajikistan, Cuba, The US state of New York and The US state of Vermont
Kraken proof of reserve
A Proof of Reserve (PoR) is the reported state of invested assets. It is important to check it to verify the solvability of a crypto exchange. Check it out.