Hi,
Looking back into the past it seems that coins with promising technology were always among the best performing coins, especially if they stared with a small market cap. 

Examples for such coins:
XBY
XEM
IOTA
EOS
Byteball

At least three of the mentioned coins are already mainstream. Only XBY and Byteball can still somehow be considered undiscovered.

What other still undiscovered coins with promising technology do you know that will probably appreciate a lot in price in the future?
You can also include coins that do not exist yet.