Looking for a modern brand guidelines solution for a growing ecommerce startup - any recommendations?

I'm an in-house designer at a 2-year-old ecommerce startup, and my marketing lead wants me to find a better way to scale our brand guidelines. PDFs just don't work for us anymore, our marketing is slowly moving heavily towards motion and animation-driven due to social media, and we need something that can actually communicate the output and guidelines.

Version control is also becoming a mess with external partners and vendors constantly using outdated assets.

We've looked at Standards and Corebook but want to know what else is out there. Budget is always a concern (as it is for every startup), so ideally something that doesn't cost an arm and a leg.

Anyone have recommendations for tools that actually work?