Litecoin (LTC) is one of the leading alternatives to the still inviolable Bitcoin.
It is the second currency ever created, back in 2011. The market capitalization (quantity in circulation) is 65 million, which currently puts it in 7th place in the list of the largest cryptocurrencies.
Like any currency, it is not issued by the government or the central bank of any country. Instead, it is powered by blockchain technology, which on paper guarantees a high level of security and efficiency. The concrete outcomes, however, depend on the quality of the LTC implementation on the concrete blockchain.
Bitcoin may still be the gold standard, but many believe that LTC is already establishing itself as "digital silver". He certainly has great potential.