Have they done so poorly? There aren't that many mainstream OSes, period, and there's not a lot of a space for a new OS. In embedded computing, various commerci

Have they done so poorly? There aren't that many mainstream OSes, period, and there's not a lot of a space for a new OS. In embedded computing, various commercial sectors such as aerospace, and the military, there are highly successful microkernels most people don't know about -- QNX is the most well known example, but there are also others such as Integrity, and L4 and its many variants are heavily used in embedded settings. L4 runs on tons of small devices, including the iPhone, and is probably the most successful microkernel in existence. Not "niche" by any stretch.