Windows Phone 7.5, known as Mango, is a massive upgrade to the already impressive Windows Phone platform, including major additions like multitasking, fast app switching (along with threaded conversations, an idea taken from the deceased WebOS), a totally new browser, apps integrated into search, augmented reality, and way more. It's the biggest update since the platform's original release, and we're really looking forward to seeing the next wave of hardware that really takes advantage of it.
Mango is rolling out today to most Windows Phone 7 phones, completing the rollout over the next few days. The next wave of hardware, including the first Nokia-built Windows Phone, should be coming later this fall, so stay tuned for a review of that. Check out the Windows Team Blog for more info.