The Gemini Gyro by Yomega is a yo-yo first released in 1990. It features a transaxle for long spin times, but its defining gimmick, is that it could be converted into a spin top and back. It is done by unscrewing the halves, and putting a special plastic shaft, referred to as the "power converter" on one of them. To make the top spin, the user would wind the string around the power converter, insert the yo-yo half with the axle into it, pull the string swiftly and lift the axle half off of it.
The 1992 release of the yo-yo came with three Flash Discs that could be put on the top, so that the top would make dazzling effects as it spun. The final version of the yo-yo was based on the design of the Power Spin, before the Gemini Gyro was redesigned to be a gyroscope toy.
Sadly, the Gyro Gemini yo-yos did not do too well in the market, and is difficult to find these days.