Geartronic is a transmission option, based on the Tiptronic design, offered in many late-model Volvo vehicles, mostly in the high-end passenger cars but also appearing in some of their long-haul tractors.
It is designed to be an alternative to those who like the convenience of an automatic transmission and the control of a manual transmission. It is based on the Tiptronic design which means it is essentially an automatic where the gear is user selectable. The process is simple, much like an regular automatic transmission, where the gear selector is moved to engage the transmission, but from there the shifter is nudged in one direction to up-shift and another to downshift.
One "feature" of the Geartronic gearbox is that, like an automatic, while it will downshift as the engines' RPMs get too low to avoid "killing" the engine, it will not up-shift automatically; this is because, under many circumstances, the engine can deliver more power at high revs, and so the transmission leaves up-shifting as an exercise to the driver. There is, however, an RPM limiter so the engine will not be overreved and blow out should you forget that up-shifting is necessary.
Obvious upsides are the control and fun of a manual with the ease of an automatic; Volvo states that there is no little difference in gas mileage between vehicle with a Geartronic gearbox or a regular manual gearbox, though this is doubtful because the system uses a Torque Converter. Noted downsides are lack of fine control due to the lack of a clutch, especially during reverse maneuvers, and a "noticeable" lag when up-shifting at high speeds.