What are the different types of Penny cryptocurrencies?

Could you elaborate on the various types of Penny cryptocurrencies that are currently circulating in the market? Are they all based on similar blockchain technologies, or do they vary significantly in their underlying protocols? What are some of the key factors that investors should consider before investing in Penny cryptos, given their volatile nature? Also, how do Penny cryptos compare to major cryptocurrencies like Bitcoin and Ethereum in terms of market capitalization, liquidity, and potential for growth? Additionally, are there any specific industries or use cases where Penny cryptos are gaining traction, and how do they differ from each other in this regard?