this is pretty well known, and can be played orally as "Think Fast" (see below.) Otherwise, give students a time limit (between 15 and 45 seconds works well to keep everyone engaged and keep it "pacy" - but you can give longer limits if your students have the vocabulary and the attention span!) - I give a different limit each time, and don't always warn students how long they will have.
Give a category (things that are usually red, activities that don't involve a ball... the more creative the category the better, but you can stick with standard MFL categories such as words beginning with..., things you'd find in a classroom) and call out your "start!' word (in the target language.)
Students write down as many words as they can think of that fit the category. Students get one point for each correct word they have written by the end of the time limit.
A variation: Once you have stopped them (at the end of the time limit), ask the student who has come up with the most words to call out their words. If they call out a word that others have written down (they call out to say) doesn't count. All students need to cross out any words that anyone else has also written - this means students start getting creative and thinking laterally about what words to write down.
Another variation: as a team game. Give a longer time limit, and each team has one pen and one peice of paper. The paper can be sticky-taped up on the wall (each piece away from the others so that the other teams can't read them!). Students are grouped on the other side of the room so they need to run to the piece of paper, write down their word then run back to pass the pen on to the next person.
Of course, there are lots of other ways to adapt this one - please add your version as a comment below!