Least successful...

In a nutshell, an multi version http client for a elasticsearch.

It supported ES 1.7 up to v7.

With an reduced future set, but all in all it allowed doing everything ES offered - just not for one version, rather the whole monty.

For various reasons I wasn't allowed to opensource that...

Which brings me to the least successful part. The client is a beast and would be a blessing for a lot of people I'd guess, but it's sadly covered by more legalese than one could imagine.

Think of legalese as in "Angel - Wolfram and Heart" legalese. I wouldn't be surprised if some part of the contract was written in blood.

... And least successful as in: Nope. Never gonna do that again.

Abstractions necessary for supporting multiple versions are are really painful.

Having an E2E test suite consuming > 64 Gigabyte of RAM for testing against several ES docker instances in parallel isn't fun.

Nothing of that project was fun.

Still gives me nightmares.

(NDA expired short time ago)