Main cryptocurrencies whitepapers

Bitcoin: https://bitcoin.org/bitcoin.pdf

Ethereum: https://github.com/ethereum/wiki/wiki/White-Paper

Ripple: https://ripple.com/files/ripple_consensus_whitepaper.pdf

NEM: https://www.nem.io/NEM_techRef.pdf

IOTA: https://iota.org/IOTA_Whitepaper.pdf

NEO: https://github.com/neo-project/neo/wiki/Whitepaper-1.1

Monero: https://github.com/monero-project/research-lab/blob/master/whitepaper/whitepaper.pdf