Bhakti yoga, the yoga of devotion. However, it can also be seen in a more practical light.
Some people claim that chanting has health and spiritual benefits due to the vibrations it sets up in the body and brain. Even if that isn't the case, chanting can be a positive form of meditation. It has similarities to breath meditations, as the act of chanting requires us to focus on our breath, which we hear as sound and feel as vibration, as well as through the movements of our lips, tongue and vocal chords. The repetition of a chant sets up a structure to occupy our monkey mind, so that it doesn't have as much chance to drag us off in different directions.
Certainly, if you've tried meditating but find it hard to concentrate or to follow visualisations, it might be worth giving chanting a go. And if you enjoy other types of meditation and like singing, it could be one to add to your repertoire. You don't have to "be able to sing" in order to chant, many chants are more like speaking while staying aware of your breath. The only thing you do need is a time and place where you won't feel self-conscious if someone hears you ;)
To get you going here are a selection of chants, some more musical, some more spoken. To start, you can chant along.
Deva Premal - Gayatri Mantra
Om mani padme hum
Jai Uttal - Durga Pahimam
Donna De Lory - He Ma Durga
Later, you may find you like to pick a chant and go for it. It's not about sounding great, or even being loud. You can experiment with almost whispering, or seeing how much your chest or head can resonate. The main thing is for your focus to be on your breath and the chant. If you give it a go, I'd love to hear your experience!