windows 8.1 for mobile phones
Apart from the lack of developer love win 8.1 was quite a decent os. If only Microsoft persisted things could have been different. It was the little things like finger print support, proper email client, printer support that made me return to Android. They had a sweet os that ran like the blazes on lesser hardware, was secure, and had good battery life, not to mention those Lumia cameras were the best at the time. And they pissed it all away.