Arduino with nRF24L01 I am using nRF24L01 with Arduino Nano and Mini. I feel they are very useful when we want to connect multiple Arduinos together. 

In market we can buy Arduino with WiFi and Bluetooth, why don't they make Arduino model with nRF24L01? Is there any specific valid reason?

Or am I wrong in using nRF24L01 and there is a better cost and power efficient way to connect multiple Arduinos together wirelessly?
NordicRF (the company behind nRF24L01) has released two series of SoC devices that are compatible with nRF24: NRF51 and NRF52. Thanks to the effort by Sandeep Mistry and other contributors, they can be programmed using the Arduino IDE and libraries. Instructions are available here: https://github.com/sandeepmistry/arduino-nRF5

I have tested NRF51822, which is the cheapest variant (costing slightly more than Arduino Pro Mini + NRF24L01+ but in a single small and power-efficient package) and it works great.

The BBC Micro:bit is based on NRF51. More information is available at https://forum.mysensors.org/topic/9722/bbc-micro-bit-and-mysensors-a-great-match

Compared to the Atmega328-based Arduino Pro Mini, NRF51822 has 8x larger flash and 8x larger RAM. It also has Bluetooth 5 and BLE support and a 32-bit ARM Cortex M0 CPU.

There is also this alternative: https://www.ebid.net/eu/for-sale/arduino-ide-compatible-controller-with-the-nordic-nrf24l01-radio-transceiver-156695123.htm

Specifications:


Dimensions 59mm x 18mm
The Nordic nRF24L01+ 2.4 GHz Radio transceiver on board
Supply voltage up to 6.5 Volts
The Digital and Analog pins are 5 volts
ATMega328P frequency is 8 Mhz
4 battery connector pins
FTDI header for programming



Full disclosure: I am member of the MySensors core team. A MySensors user (not affiliated with the core team) created and is selling this board.