BLE Nano 2 is the smallest Bluetooth Low Energy System-on-Chip (SoC) development board. You could develop application using Nordic's SDK, mbed.org or the open source Arduino Library for nRF5x.
This Kit include a companion board, DAP Link v1.5, which is used to load firmware into BLE Nano from a PC. The DAP Link has an ARM Cortex-M3 MCU and is used to program and debug an application running on Nano 2 via SWD. DAP Link is an open source project by ARM mbed team, check it to learn more about DAP Link.