Alternatives (which are open source) to KDB+ are split into two categories:
New Database Technologies (tick data store & ASOF JOIN): Clickhouse & QuestDB
Local Quant Analysis: Python – with DuckDB & Polars
Some personal thoughts:
Q is very expressive, and impressive performance can be extracted from kdb+, but the drawbacks are proprietary formats, vendor lock-in, costs, proprietary language and reliance on external consultants to make the system run adequately, which can increase operational costs.
I'm personally excited to see the open-source alternative stack emerging. Open Source time-series databases and tools like duckdb/polars for data science are a good combination. Storing everything in open formats like Parquet and leveraging high-performance frameworks like Arrow is probably where things are heading.
Seeing some disruption in this industry specifically is interesting; I think it will be beneficial, particularly for developers.
NB: disclosing that I'm from questdb to put thoughts in perspective