Better to cite github project or web page of unpublished software? In my research, I am using several compression algorithms that do not have a related publication. For example Facebook's lzfse. Would it better to cite it's active github project (e.g., https://github.com/lzfse/lzfse) or blog or other web content introducing this utility (e.g., https://developer.apple.com/reference/compression/data_compression)?

I guess I am concerned with the amount of time this will stay active online as well as relevance.
As a reader, I would find a citation or mention of both resource types to be useful, especially in the all-too-common event of a link breaking or a github project going dormant. If you're concerned about formality then contacting the original authors to determine which citation they would prefer would be helpful. Otherwise, as long as your audience knows what you're referencing and where to find out more about it, you should be fine.