simplystats

Also I think your model of "buying" a free copy is a great idea. Then if you think the content is worthwhile consider the second purchase a donation.

I dunno but I'm the author and I think it is pretty useful :). The guides have hundreds/thousands of stars on Github and I think some folks found it useful.

I'm using this publishing model because that is how modern scientists do it - avoid the traditional publishers so you can offer content for free or relatively cheap.

Didn't say I used it for blogging :)