This app is a serial monitor that makes it possible to send string in UTF-8 ,HEX, decimal, Octal or binary format between an IOS device and an device equipped with BLE Bluetooth module. 
When the app is started an available BLE device can be selected. With several options one can optimise the communication.
With programmable buttons command can be sent.
Alarms can be set on texts in the received strings.
In the support link several Arduino source codes can be found that make uses of this app.

This program was known HM10 Bluetooth Serial Pro.
Because the programmer quit developing IOS programs EdSoft continues offering this beautiful designed app free with the name is this store. The Pro version also connect to nRF BLE devices like the ESP32 and Arduino equipped with Espressif BLE MCU's
See examples here: https://ednieuw.home.xs4all.nl/BLESerial/BLESerialUsage.html