There used to be a number of "alternative" wikipedias made by people who didn't agree with the editing and administrative decisions of Wikipedia. It's hard to find them now. The one I visited I found via its link from a wikipedia article that was removed.

I do not observe leftist bias in wikipedia myself, it more looks like general mainstream bias of the powerful and formally educated. Far-left information is also removed and replaced with citations to published propaganda. You can defeat individual situations if you make them your crusade in its system.