What you meant "Stable" coins - Do this mean its price does not change much? Or about "Stable" technology.
If you are talking about the price then I think there is no such coin in the crypto market - there is no coin that its price is stable. => If you want stable then keep your money in your poken (USD). LOL
If you are asking about the technology/platform, I suggest you to invest in Ethereum!
He is probably talking about coins that are never increasing in price (well, a little) and are NEVER going, but this is more than impossible.
The most stable coin is Tether..
Tether doesn't even backed by dollar and it's pure manipulation in my opinion. But it seems there are some projects develop their own stable currency based on their own formula to decrease the volatility after it has already listed on the exchange site. Tether looks a bit shady right now.