Thank you for playing and for your extensive comments! The graphics do not represent a specific machine, but are inspired by 1980's machines like the VIC-20, ZX Spectrum and Commodore 64. You are right that the UI is clunky, it needs some work!
You are correct that there is no leveling up implemented yet. The game strategy is to kill some monsters, get gold/valuables, buy the best armour you can (plus some healing potions) then slog it out with the tougher enemies (which can take time). I hope to develop a more sophisticated RPG in future, with faster combat rules.
Re the dragon stones, you can try to sell them but game doesn't let you, because their price is listed as 'n/a'. Sorry if that caused confusion!
Thanks again for trying out my game!