Facebook's On This Day and other nostalgia-driven posts are helpful for reminding you of moments from years past, but they eventually drift out of your News Feed. What if you want to revisit them at any time? You can now. The social site has launched a dedicated Memories section that collects all those souvenirs and anniversaries in a single place. It also includes previous "Memories You May Have Missed" and "Recaps" features that respectively help you catch up on milestones and summarize a busy season.