( Note: This article is a work in progress, and needs to be added on to. )
Tix were a currency similar to ROBUX that you could obtain for free. Before they were removed, you got 10 Tix every time you logged on, and 1 Tix every time someone joined a game you made. Tix could be used to buy things that could normally cost ROBUX, but could also buy some things that ROBUX can't, and it could not buy certain things with ROBUX. Tix could also be used to purchase player-made products if the product's creator chose to allow it.
You were also allowed to convert Tix to ROBUX. 10 tix would be equal to 1 ROBUX, as ROBUX had more value and could buy more things, such as limited hats.
However, Tix have recently been removed by ROBLOX, as they stated that people were exploiting the systems of gaining Tix in order to get a large amount that they could then do whatever they choose with.