Bitcoin, the first and most popular cryptocurrency
Ethereum, the blockchain that is the Web 3.0. Currently the most advanced blockchain out there.
Ripple is a USA company behind the XRP cryptocurrency. XRP was originally intended as a layer for settlements across borders between banks - a kind of SWIFT replacement.
Cardano is the technology platform running the ADA cryptocurrency. Like many others, it promises to be the "Ethereum killer".
Qtum is an intermediary blockchain designed for interoperability and communication between other blockchains. Qtum is managed and developed by the Singapore-based Qtum Foundation, and their main business model is helping companies implement decentralized applications. Qtum combines the robustness of Bitcoin Core and the versatility of the Ethereum Virtual Machine to produce a stable but flexible communication layer between the blockchains.
Verge, a fast and cheap cryptocurrency with a focus on privacy.
Peercoin is one of the first Proof of Stake coins.