Letterbox

From BoardGameGeek:

Letterbox is a 1+ player game about making words. Each player receives 5 double-sided square cards with a letter in each corner of the card. Players shuffle the cards and then begin play. They are allowed to rotate the cards, but not change their positions in the hand. Importantly, as long as the cards are all on their light side or all on their dark side, it is always possible to find a word no matter what order the cards are in. In the solo variant, players have special challenges and additional rules to make the game more challenging. -description from the designer