Jodel is the main replacement to my knowledge. There might be others too, but I don't think any of them have caught on very much. It's a shame because there definitely still is a market for a yikyak clone, but I doubt investors are going to be very bullish about one.

I think the main reason anonymous social media is out of favor is that it's hard to monetize. It's hard to gather information (and thus serve valuable ads) about your users when they are explicitly using your app to not share that information. When yikyak introduced profiles, I think that was when everybody stopped using it.