duolingo websites -lrb- `` websites '' -rrb- and mobile applications , including the tinycards application -lrb- `` apps '' -rrb- and related services -lrb- together with the websites , the `` service '' -rrb- , including our language proficiency testing services -lrb- the `` duolingo english test '' -rrb- are operated by duolingo , inc. -lrb- `` duolingo , '' `` us , '' or `` we '' -rrb- .