I purchased a purple Shanghai subway card with the deposit of RMB 20. Does this card work in other cities, such as Beijing or Tianjin?
Officially, or at least from Wikipedia:
As of June 2006, the card has been interchangeable with the Wuxi Tai-Lake Transportation Card, and can also be used in Suzhou.
So it can be used in at least one other major city. It doesn't look like it'll work in Beijing, however.