Many of the X-Pack features are actually available in their "Basic" license and even public source: https://www.elastic.co/what-is/open-x-pack but just not under an actual OSS license.

e.g. "Data Streams" is covered under the Basic license so you can use it for free (I think? As far as I can tell at least). You can find the feature on their subscriptions page: https://www.elastic.co/subscriptions

I find the whole situation with X-Pack, Subscriptions and OSS vs Basic super confusing and the subscription page seems very bad at explaining it all.