Help me find the os for my raspberry pi model b+
There have been more OS.
- Linux branch, Debian, CentOS, FreeBSD, Ubuntu,
- CMSIS supported, Mbed OS,
- Kind of RTOS, zyphre, rt-thread
- Windows IoT
- Android Things
Since it is based on ARM-Ax, nearly everything can be ported. And more can be added to this list.
I use Raspian exclusively since taking a slice in the model of a Pi B.
I have yet to find a reason to explore other O/S's.
You forgot Windows 10 IoT. Actually, maybe you didn't. I tried it and unless you're really tied to an application it's not really ready and probably never will be.
Seriously though - it will depend on what you're doing with the Pi.