I would buy coins under 1$. New coins are added every day on coinmarketcap. I know is not to munch 50$ dollars, but I know someone who invested 10$ dollars in a coin, he buy 1000 coins with 0.01 cents and now that coin is 10 dollars. Calculate yourself what profit he makes. I don't say that every new coin will be 10 dollars, but anyway can make a profit.

Siacoin at the moment. 

Or an ICO like NVT Novablitz - if you can stretch to the 0.1 ETH limit on it - a lot of potential.

More information on that here:

https://novablitz.com 
https://t.me/novablitz

Would invest in a promising coin with a small value - Ripple, Stellar. For a long time in Bitcoin, Ethereum, Bitcoin Cash.

Neither Ripple nor Stellar are small value, both are above $4B marketcap. There is a huge difference between low value per coin and total market cap. The only reason these 2 coins are "cheap" is because the supply is so big.

The amount is really small. But if you know what to bet, you can increase the profit several times.
Recommend inexpensive and promising coins - Wagerr. Now it 0,335$. In the summer I bought it for 0,07$ for them. Today he brought me +360%. But the main events are expected in mid-January, 2018. I think you should not split such a small amount for a few coins, as I will have to wait very long for profit. Bet on one thing. And gradually increase its portfolio of new coins.

If I had $50 only I wouldn't invest I would be looking to trade it up to a greater amount, I think with investing you're very limited with how much you can earn so I would look to trade it up.

I wont invest it,because its not an investment for me $50 will only pay your transaction fee in exchanges,you are not doing investment you are just wasting your time and money.

if you only have $ 50, then you can buy a coin on an ICO
and wait a few years. and you will have a small chance to make big money.
 to make money on the crypto, you must first make money elsewhere

I would put 50 into dgb and lbry I think those two will do well in the next 6 months and are likely to make profit.

in my opinion buy some cheap altcoins, such as shield xsh, Neo, Wabi  or deep onion.