Are there real-life alternatives to the chain+derailleur combo? I was reading an article about the CeramicSpeed’s Driven concept and, while not interested in the efficiency part, the chainless system reminded me of something I was wondering for some time: are there real-life alternatives to the chain + derailleur combo?

By "real-life" I mean a solution which is reasonably commercialized. I realize that there is nothing obviously replacing them as I do not see them at my Decathlon shop but there may be something a bit less mainstream which is still in use.

My main concern is the complexity of the derailleur system  coupled with a chain which breaks - and all of this requires maintenance. 

An analogy would be the engine in petrol cars together with the mechanics to bring the couple to the wheels vs a Tesla solution where a small, one-block electric motor sits directly on the wheels axis (Note: I am not thinking about replacing the power source (that is me) by an electric system, just to show how the complexity has been reduced in a tesla vs my regular car. I still want to pedal, less the maintenance and system complexity)
Belt drive + Internally Geared Hub is a popular combination.

Existing systems are based around a gates carbon belt drive. See the Breezer Beltway series bikes. Also Reeb Cycles began offering belt drives for mountain bikes when they first came to market.

Also, now there is a breakable belt system called Veer that doesn't require a frame cutout (though uses cogs somewhat different from older belt drive systems) which could be used in configuration with an internally geared hub (when their new pro-version comes out). Currently it appears to be singlespeed only. 

Though this is still rather similar to a chain drive system, there is less regular maintenance needed to keep the drivetrain clean as wear is not as damaging on the belt drive system. Performance is different with an IGH hub though. 

There are also shaft driven bikes which engage with a standard internally geared hub (instead of a cassette like mechanism). See related SE question with some detail. Any experience with shaft driven bikes?