What are Penny cryptocurrencies?

Could you elaborate on what penny cryptocurrencies are and how they differ from more established digital currencies? Are they seen as a viable investment option for those looking to enter the cryptocurrency market with a smaller budget? What factors should investors consider before investing in penny cryptocurrencies, given their volatile nature and potential for significant price fluctuations? Do penny cryptos offer any unique advantages or opportunities compared to larger, more established coins? How do their market caps and trading volumes typically compare to those of major cryptocurrencies?