wiki.volkszaehler.org

original manufacturer's app: https://play.google.com/store/apps/details?id=wit.android.ble.smartenergymeter
conrad's app: https://play.google.com/store/apps/details?id=cei.android.ble.smartenergymeter

[~/WiTenergy]$ ls -l *apk 1069410 cei.android.ble.smartenergymeter.apk 1107808 wit.android.ble.smartenergymeter.apk

the whole thing seems to be based on TI's „sensortag“:

[~/WiTenergy]$ unzip -l wit.android.ble.smartenergymeter.apk 
  Length      Date    Time    Name
---------  ---------- -----   ----
   126976  2014-10-18 01:36   assets/SensorTagImgA.bin
   126976  2014-10-18 01:36   assets/SensorTagImgB.bin
[...]

[~/WiTenergy/wit.android.ble.smartenergymeter]$ grep -iE texas\|ti\|sensortag assets/*
assets/about.html:<meta name="Author" content="Texas Instruments" />
assets/about.html:<title>About BLE SensorTag</title>
assets/about.html:    <p><b>BLE SensorTag application</b> from <b>Texas Instruments</b> displays converted values from each of the six sensors
assets/about.html:    in the SensorTag. It also visualizes button presses. Up to four sensors may be used simultaneously (including keys).</p><hr />
assets/about.html:    <p class="copy">&copy; 2013-2014 Texas Instruments</p>