It's not a complete replacement, but if you're in a Python ecosystem, you might find Moto to be of interest.

https://github.com/getmoto/moto

at least some parts of localstack seemed to be built on moto, based on a brief look at some point

They were, but they moved off them - probably with a move away from OSS as a long term plan.

I've used Localstack extensively for ~7 years, and I will rejoice when I can finally be free of it. I've found it to be low quality software, and full of bugs.

Oh, the irony

AGPLv3 attempts to solve this problem, by forcing SaaS providers to open-source their modifications.

https://www.gnu.org/licenses/agpl-3.0.en.html

Depends on the needs of the licensor. AGPLv3 solves the problem of other players taking the code, improving it privately, and not sharing those improvements. But AGPLv3 is not a silver bullet for people who write Open Source code and pretend to make a living from it. "Open Source is not a business plan".

https://news.ycombinator.com/item?id=45095581

There is also the use case of delegating tasks programmatically to an LLM, for example, transforming unstructured data to structured data. This task often can’t be done reliably without either 1. lots of manual work, or 2. intelligence, especially when the structure of the individual data pieces are unknown. Problems like these can be much more efficiently solved by LLMs, and if you imagine these programs are processing very large datasets, then sub-millisecond inference is crucial.

Aren't such tasks inherently parrallelizable?