I have found this https://github.com/OpenMage/magento-lts (OpenMage/magento-lts) and I am wondering if this is "official" or something.
No, there's no official git repo that accepts bug fixes for Magento 1.x
As Raphael said, nothing official, but ...
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http://github.com/OpenMage/magento-lts is the only active maintained fork - since years. IMHO i'd prefer LTS over vanilla Magento by far. The are a lot of years old known bugs in Magentos bugtracker, that are fixed in this project. Some issues that were raised here at MSE.
@kanenas well it's up to you, you can definitely use it but as it is not official and not reviewed by the Magento team, you have no garanty that the bug fixes are clean / not introducing more bugs.
You're right. No official reviews, but at least two reviewers. No, not prefect and not 100% fail safe, but still far better then plain Magento 1 with no feature fixes/performance improvements since 2014 ...