This is the Shimano S-T-T-X-3-0-7-R gear shifter.
This Shimano shifter is a seven speed, meaning it has 7 different shifting levels. On the surface, you have one large lever that you push with your thumb to shift up into low gear, and then there's a button that you can push that'll index through all seven gears to the highest gear. This Shimano shifter comes with an extra long cable and housing to fit on our longer frame bikes. It can be customized to fit on any length bike.