TTL = transistor transistor logic

This is the technology in the common 74' series integrated circuits that became popular in the late 1960's and 1970's. You can get basic IC's that perform AND, NOT, XOR operations but also more complex IC's that perform as multiplexors, buffers, registers and so forth. You can find these in computers like the PDP or VAX series machines.

They are not used as much today and so less of them are still manufactured.