It's difficult to determine an exact number of altcoins, as new ones are constantly being created. However, it is estimated that there are thousands of altcoins currently in circulation. Some of the most popular altcoins include Ethereum, Binance Coin, Dogecoin, Cardano, XRP, Litecoin, Chainlink, Polkadot, and Stellar. Each altcoin has its own unique features and use cases, such as smart contract functionality, faster transaction speeds, or improved privacy. While Bitcoin is still the most well-known and valuable cryptocurrency, altcoins have gained popularity in recent years and have become an increasingly important part of the crypto market.

Total Number of Altcoins:

High estimate: CoinMarketCap lists over 22,900 cryptocurrencies, which would encompass all altcoins and other digital assets.
Lower estimate: However, many of these might be inactive or have very low value. Considering only actively traded and relevant ones, figures range from 8,000 to 10,000.

Popular Altcoins:

Popular altcoins can vary depending on your criteria, but some with consistently high market cap and usage include:

Ethereum (ETH): The second-largest cryptocurrency after Bitcoin, known for its smart contract functionality and widespread adoption in decentralized applications (dApps).
Binance Coin (BNB): Utility token of the Binance exchange, widely used for trading fees and other benefits within the Binance ecosystem.
Tether (USDT): A stablecoin pegged to the US dollar, often used as a safe haven during market volatility and for facilitating cross-border transactions.
Cardano (ADA): Focuses on scalability and sustainability, utilizing a proof-of-stake consensus mechanism.
Solana (SOL): Known for its high transaction speed and low fees, attracting attention in DeFi and NFT spaces.
Polkadot (DOT): Blockchain interoperability platform aiming to connect different blockchains together.
Dogecoin (DOGE): Originally a meme-based cryptocurrency, but has gained notable market cap and acceptance.