A T-Chart is basically an input/output table. When you have a value on the left side, you do something to it (add 5, subtract 3, whatever...) to make the number on the right side. It is a table to show functional relationships.
I've also used for literature. EX: Fantasy on one sise, reality on the other. Fact on one side, opinion on the other, etc... The kids would come up and place a card, or write it, under the appropriate column.