Tomorrow 07 Feb 2017 NuttX RTOS will complete 10 years as an Open Source project. The projects was published in the SourceForge on 07 Feb 2007.
From 2007 to 2017 NuttX evolved a lot. Maybe you don’t know, but NuttX is used by many companies. If you have a Moto Z Phone and got a Snap cover that Snap run NuttX!
Other example is Sony (that company that inspired Steve Jobs to create great products) is also using NuttX and even did a publish presentation about the benefits of using NuttX: http://events.linuxfoundation.org/sites/events/files/slides/DevelopingAudioProductsWithCortexM3NuttXC%2B%2B11_LFELC_OpenIoT_ishikawa_20161209_0.pdf
Also I created a YouTube channel dedicated to NuttX, called NuttX Channel:
NuttX is evolving fast and will be a Linux companion on “Embedded Arena”.
There is no other RTOS good like NuttX, you can spend your time searching. There are more than 200 available: https://en.wikipedia.org/wiki/Comparison_of_real-time_operating_systems
Thank Greg Nutt for this incredible RTOS called NuttX.
More here: http://www.nuttx.org