Next to the quest button it says "complete quests, get rewards", where it should say "complete quests; get rewards".
If you hover over "Donate" it will say "Help the developers to keep Element Free making a donation through paypall, it's secure and every penny counts." where it should say "Help the developers keep Elements free by making a donation through paypall. It's secure and every penny counts."
I'll find more when my grammar nazi re-awakens.
to be fair, they could use a semicolon as well
As for actual spelling mistakes, when the Oracle gave me Schroedinger's Cat as a pet, it read "Schrdinger's Cat." What a bummer.