The SX52 Processor was one of a line of 8 bit microcontrollers designed by Ubicom. It was based on the PIC architecture and housed in a 52 pins package. When Parallax, inc. took over the SX line of microcontrollers they could not support the 18 and 52 pins packages so the SX18 and the SX52 processors became obsolete. Currently SX processors are available in 20, 28 and 48 pins packages. Ubicom is still the manufacturer of the dies, but sends them to Parallax for packaging.
References
SX52 Processor Wikipedia(Text) CC BY-SA