For Phelps, it was his record 21st Olympic medal and 17th gold of his career. Phelps was next to last at the turn but then produced his usual furious finish to clock 51.21 seconds in the 100-meter butterfly. After his win, Phelps said his last individual race was "really special."
Phelps will end his career with the 4x100-meter medley relay Saturday.
Franklin set the world record in the 200-meter backstroke final by nearly a second, winning her fourth medal and third gold of the London Games. Ledecky, who at 15 is the youngest U.S. swimmer in London, nearly broke the world record to win gold in the 800 freestyle.
Roger Federer won the longest tennis match in Olympic history, beating Juan Martin del Potro of Argentina in the semifinals 3-6, 7-6 (5), 19-17 in 4 hours, 26 minutes.
A four-time Olympian, Federer clinched at least a silver. On Sunday, he will play in the final against the winner of the second semifinal between No. 2-seeded Novak Djokovic of Serbia and No. 3 Andy Murray of Britain.
In 2008, Federer and Swiss teammate Stanislas Wawrinka won the gold in doubles, but he has never won a singles Olympic gold - the only major prize he has never won.
In women's tennis, Serena Williams clinched her first Olympic singles medal, beating No. 1-seeded Victoria Azarenka 6-1, 6-2. On Saturday, Williams will face first-time Olympian Maria Sharapova, who beat Russian teammate Maria Kirilenko 6-2, 6-3.
Serena and Venus Williams have a chance to clinch at least a silver in the semifinal match scheduled later Friday. The sisters won the gold medal in doubles in 2000 and 2008.
In women's soccer, the U.S. team has advanced to the semifinals after defeating New Zealand 2-0 in the so-called "knockout stage" of the quarterfinals. Abby Wambach put the Americans up 1-0 in the 27th minute, and then Sydney Leroux from Los Angeles gave the U.S. an insurance goal in the 87th minute when she carried the ball over virtually half the length of the field for an impressive finish.
The U.S. will face the winner of Friday night's match between Canada and Great Britain in the semifinals.
Despite losing her match, a judo fighter from Saudi Arabia is still being hailed as a hero. Wojdan Shaherkani is the first ever female Olympian from Saudi Arabia, and she only competed after a compromise allowing her to wear a modified hijab, or head covering.
She lost her judo match in just 84 seconds, but received a standing ovation.
The second Saudi female athlete, Sarah Attar will compete in the 800 meters, which starts next Wednesday. She had dual citizenship in the U.S. and Saudi Arabia and attends Pepperdine University.
It was a sad day for Qatar's first female Olympian. Al Maki, 17, pulled a hamstring at the start of the 100-meter dash and was reduced to tears.
Gabby Douglas, who won the top prize in gymnastic on Thursday, has already landed a major endorsement. The 16-year-old Olympic gold medalist will be featured on a special edition Corn Flakes box, which will hit stores in the fall.
The Associated Press contributed to this report.