What you're most likely looking for is amateur (ham) radio. The exactly regulations will vary by country, usually there's some sort of testing/licensing required (at least if you want to transmit, you can listen without a license)

I didn't look too far into it but it looks like the app you linked is basically a tool to let you use your phone as a controller for other radio equipment. You'd probably need to be licensed to actually use it, and there's a good chance the equipment needed is pretty pricey. Ham equipment can kind of run the gambit from handhelds that run from about $20 up to thousands of dollars depending on what you want to do with it. You're probably better off starting with some more standard equipment before you start trying to rig together other stuff controlled by an app.

There's a lot of info out there for free on the internet and plenty of books have been written about how radio, so there's a lot of resources out there to learn from, or if there's a radio club in your area (there usually is) you can show up to a meeting and ask some questions.

Assuming you're in the US (different countries again have different laws) there's a few other radio options if all you want is to talk to people who are local to you. You can get a CB radio (think Smokey & the Bandit or truckers talking to each other) some places have more or less people actually using CB radio. The range and capabilities are more limited than a lot of ham options, but you can usually count on a few miles of range, and sometimes it's nice to get a heads up from truckers about traffic issues and speed traps and such. I personally like to use them with friends in different cars when we're on a road trip.

There's also FRS radios, you can pick them up pretty cheap at Wal Mart, pretty basic walkie talkies.

Many of those FRS radios are also GMRS radios, there's a GMRS license needed to use the GMRS capabilities, not test, just a licensing fee, so that's something to be aware of.

MURS radios also exist, I honestly don't know too much about it, but it's another free, no-license radio service you can use.

Each of those have their own limitations and restrictions on what you can do with them, but in probably 99% of cases you're probably not gonna run afoul of the law if you don't try to modify the radio or do something obviously stupid and use it in a way that's not interfering with other people's uses.

Yeah, ham radio. If I was doing it all over again, I'd go for the most basic SSB radio I can find that plugs in to a computer sound card - that should in theory be able to do anything reasonable. You'll also need feed lines, an amp and a large-ish antenna, which is where things get a bit more technical hardware-wise, especially if you're in an apartment or have something like an HOA, but it nothing you can't figure out.

And yes, a licence. So far I've found the requirements pretty reasonable in my jurisdiction, they relate to not frying yourself or your equipment, and how not to be a menace to other people sharing the radio bands. You used to need to learn Morse code fluently enough to pass a practical test, but most places have gotten rid of that.

If you're using wifi, you're technically doing it right now!

To go along with all the people mentioning the need for a license for ham radio: there is a study app with literally all the questions that might be on the test and it's all multiple choice. Just keep answering the questions till you remember enough of em.

like ham radio? i think you can find affordable radios to listen, but in order communicate i recall you need like a radio communication license. at least in the USA

There are at least three legal ways to do this. CB radio, ISM frequencies and amateur radio. I say legal because the radio spectrum is heavily regulated because every transmitter affects everyone else to more or lesser extent.

You can buy CB or ISM band radios and get started.

Amateur radio is a better option in my opinion. There are many more frequencies to experiment with, people who can help and people to talk to.

Amateur licensing is different in each country, but an introductory licence is often no more than a weekend course and exam. I know of nine year olds who have done this. It's not hard. No Morse code required either.

With such a licence in hand you can use things like JS8Call, CODEC2, Olivia, WSPR and hundreds of other protocols to communicate using just a radio and a computer.

Disclaimer: I'm a licensed amateur in Australia and have been since 2010. I hold an introductory licence, here it's called a Foundation licence, and have been having an absolute blast with all that I can do.

If you have specific questions, don't hesitate to ask.

You could throw one at someone with a message attached.

Does it have to be audio? A meshtastic radio like what you get from https://www.lilygo.cc/collections/lora-or-gps will pair to a smartphone app (or browser app) and let you text with people who also have a meshtastic radio nearby. If you're in a reasonably dense area there may be several people chatting.

I realize this in not answering your question, but I thought you might like to know that some people share access to their antenna on the web at http://websdr.org/. This sdr webapp lets you listen to the airbands from their antennas basically, and each user can tune it to their own frequency at the same time.

You can start listening with a cheap Baofeng walkie talkie and a spectrum analyzer like the TinySA, if you want to transmit you will need an amateur radio license. Or depending on your jurisdiction you can start using open frequencies WO the need of a license.

If you're in the US, take a look through this website.

https://www.arrl.org/home

And specifically this link for licensing info.

https://www.arrl.org/getting-licensed