It's not at all crowded since not all of them actually work well and they are optimized for different use cases and different setups. One use case I believe is

It's not at all crowded since not all of them actually work well and they are optimized for different use cases and different setups. One use case I believe is not covered well, and I use it often, and evaluated it, is actually storing the complete time series and reading it as a whole, without any aggregation. This is important for different signal processing and so on, where sampling does not cut it. At the and I chosen KairosDB (with Cassandra backend). Not that it is perfect, but it if CRUD is most important, and you offload processing to other engines, it works well. That is why I am always looking forward to new things such as this or BTrDB. There is still a lot of room for improvement everywhere.