I use Dexcom G6 CGMS with Nightscout and xDrip+.
xDrip+ runs on Android, gets the data from the Dexcom transmitter, and sends it to a Pebble watch and also to a mongodb database.
xDrip itself supports a lot of CGMS systems, I've been using it since G4, which was not Bluetooth ready initially, so you had to build a bridge that read the data from the transmitter and sent it to the phone. Way easier nowadays,as the transmitter is using BLE.