You're correct Litecoin (LTC) is undervalued and doesn't reflect its true potential in terms of price and have lots of users/followers as well I believe. Its constantly maintaining its top position since long time where many coins came and faded away from market. I hope it will get attention as it deserve one day.
There are other projects too that are still undervalued even after having solid development. I think one of them is siacoin (SC). First data storage project existed since 2015 and still being constantly developed but I think some invisible force is stopping it from going up in term of price, suppressing it hard.
Monero (XMR) - Completely anonymous been here for very long, time and completely anonymous but never reached its full potential because the nature of it's coin became it's a negative thing in the view of governments so every country is forcing the exchanges to delist the Monero from exchanges and even recently p2p were shut down too.
Exactly XMR could have gone long way but its main feature being its own enemy and being targeted by many authorities specially by USA.