I hold Blocknet, which was founded in 2014. Still a great project which has improved a LOT the past 2 years in terms of development etc.
I'm sure they'll be back at the top once they roll out their own oracle network, which is cheaper and more decentralized than Chainlinks solution currently is.
Ethereums Infura solution, which handles dApp data is centralized as well. Something Blocknet is improving too.
I believe that Blocknet is one of the good, undervalued coins out there on the market. With years of active development and innovation, it should've been placed within the top 5 cryptocurrencies in market cap. What's most interesting about the Blocknet project is the decentralized exchange called "Block DX". So far, there's no other decentralized exchange out that focuses on decentralization at its core like Block DX. This innovative decentralized exchange aims to decentralize everything from "top to bottom" without the need to rely on centralized infrastructure whatsoever. The team is planning to revolutionize SPV too, so I'd say that Blocknet is one of those old coins that will live for a very long time.
Speaking of old coins, I try to limit myself to those that are still actively traded on the market. So far, Peercoin, Primecoin, and Namecoin are being traded on the market after all these years. The only thing is that some of these coins are not being actively developed, which makes them somewhat outdated compared to the rest of the cryptocurrencies available on the market today. But as long as there's a market for them, nothing else matters. I prefer to use old coins than newer ones because of their tried-and-tested blockchain networks. Their level of security is greater too, giving you peace of mind. Thanks to their decentralized and open source design, anyone can continue with the project's developments in order to keep the coin alive. Just my thoughts