How to colloborate and define new style guide for an existing corporate design?

As a naive ux designer, I am facing problem to define a style guide. There is existing style guide made with Adobe XD. As a Team effort we would like to improve and manage the style guide. A reasonable and productive solution is to use Frontify. Unfortunately, company runs out of budget and we need to look for an alternative which can provide same features like Frontify.

Anyone facing the same problem?