There are different apps to help manage diabetes. In my opinion, an app without a device is just a diet plan. Still, those apps are a good start to improving health.
The main focus here are the various apps used in conjunction with continuous glucose monitors and the differences in capabilities and whether they require a doctors prescription or not. Also, please remember that different countries have different regulations. Some of those that require a prescription in the US for example are Freestyle Libre and Dexcom.

This CGM requires a doctor's prescription. These prescriptions usually qualify for most insurances which is good news because the device can be a little pricey. This CGM lasts for 14 days and then it is time to change out for a new device.

The Freestyle Libre is the device I use so I am much more familiar with it than the Dexcom CGMs. This CGM has a low blood sugar alarm that alerts you when you're having a low blood sugar event. This also sends information to your phone every minute which I really like.

I believe that Dexcom was the original continuous glucose monitor and has evolved over time. It is currently much smaller and sleeker than when it started. It sends information every 5 minutes to your phone.

Dexcom 7 will last 15 days until it needs to be swapped out for a new device. This device also has a low blood sugar alarm that will alert you often times before you start to feel low glucose levels. This is a very good thing because when you are sleeping, you aren't aware that you're having a low glucose event.
There are some newer apps to help manage diabetes prevention using continuous glucose monitors that don't require a prescription. In my opinion, these types of devices can be valuable to those that don't have diabetes, yet still want to monitor their glucose activity. Lingo from Abbott labs and Stelo from Dexcom are the newer devices. These seem to be similar to the Freestyle Libre and Dexcom, yet with fewer capabilities not really needed for those without diabetes.

The Lingo, by Abbott is a simplified version of the Freestyle Libre. It doesn't require a prescription, but it also lacks certain functions such as low blood sugar alarms. It's ideal for athletes and those counting carbs. I believe it lasts for 14 days. Also, this device sends information to your phone every minute, just like the Freestyle Libre.

I would still encourage anyone that doesn't have diabetes to consider a device like this, because it will help you recognize the affects of your diet on your health. It's a good way to see the reason to start eating healthy.

Stelo is similar to the Dexcom 7 in many ways, but like the Lingo, certain functions that diabetics find important such as low and high blood sugar alarms are missing. These devices are great for athletes and those wanting to learn how to manage a healthy diet.

The Stelo is applied in a similar way as the Dexcom 7 and the Freestyle Libre and uses the same technology that sends data from the device to your phone. This CGM records readings every 15 minutes, instead of every 5 minutes like the prescription device Dexcom.

This tool helps start a healthy journey of discovering how your body responds to certain foods. You will recognize patterns and develop good eating habits and also good shopping habits. Good shopping habits are more important than we think they are.
You will find many new companies that offer a monthly subscription to their software and health program. They use either the Lingo or the Stelo because a prescription isn't necessary. The CGM is used in conjunction with their different apps. Some notify you when your levels are high and offer healthy alternatives when your glucose levels spike or fall. I think it's kind of clever to utilize someone else's product and integrate it into your own system.
I think more than anything though, it's good to learn the process of how eating carbs, fats and proteins affects us individually and to stay in control of our health. I guess all these new companies basically offering the same CGMs, but a slightly different app and diet outline is probably a good thing. It pays to shop around though so you can get the best deal. I see many companies offering different monthly premiums along with their software. If any of these interest you, try to find one that meets your needs and will do things that fit perfectly into your own lifestyle.