While not focused on OSS, this was asked 20 days ago at https://news.ycombinator.com/item?id=29662859 https://news.ycombinator.com/item?id=29662859 as "Ask HN:

While not focused on OSS, this was asked 20 days ago at https://news.ycombinator.com/item?id=29662859 https://news.ycombinator.com/item?id=29662859 as "Ask HN: Best alternatives to Google Analytics in 2021?". It listed some OSS versions there.