Bob Lee, a pioneer of financial technology who created the mobile payment platform Cash App, was stabbed to death in San Francisco on Tuesday, his family said. He was 43.  San Francisco police said in a statement that officers were called regarding a stabbing at around 2:35 a.m. in the city’s downtown area, where they discovered a 43-year-old man with stab wounds. He was subsequently taken to a local hospital but died from his injuries.  “No arrests have been made and this remains an active investigation,” police said. Officers did not name the victim, but his family identified him in statements on Facebook. "I just lost my best friend," Rick Lee wrote about his son. "Bobby worked harder than anyone and was the smartest person I have ever known. He will be missed by all those that knew him," he added. "I'm so saddened and disheartened to lose my brother," Tim Oliver Lee wrote . "He really was the best of us.…