Everything in these three solitaire games happens by 2s. All variants are free to play. No in-app purchases.
MOUNT OLYMPUS - Tableau builds down in matching suit by 2s (King takes a Jack which takes a Nine etc...). Foundation builds up by 2s.
OROS - Tableau builds down in mixed suit by 2s. Foundation builds up by 2s.
ODD & EVEN - Tableau piles hold only a single card. Foundation builds up by 2s.