There are multiple websites that list events in London. I have quite niche music tastes, and would pay a few quid per month for the opportunity to get in contact with people who want to go to the events I'm interested in.

London city or London and all surrounding small town areas? I’m outside NYC. Tons of apps in NYC market and I can’t imagine another. But the suburban market has fewer or none.

My point was that even as an avid music fan, I don’t hear a lot of folks looking for another app for this but maybe I am way underestimating what’s possible.