Are there freeware 808s that can compare
I think you're gonna have a really hard time finding a developer who's willing to dedicate countless
hours of their life to carefully studying, researching, and modelling the many
intricacies and peculiarities of a classic piece of hardware like the TR-808, who doesn't also
want to be compensated fairly for their hard work.
So either cough up the dosh for a well-made plugin like AudioRealism Drum Machine
which does the TR-606, TR-808, and TR-909 all in one convenient package, or one of the excellent plugins from D16 that you're already aware of, or simply accept the fact that samples — of which there endless
high quality packs to choose from — are the next best thing.
In my experience there isn't really much middle ground to choose from in this particular area. There are a lot of shit and poorly recorded/edited sample packs, and a lot of shit half-arsed plugins churned out by noobs in SynthEdit, but really only a small handful of truly accurate quality options to choose from if you want authentic results.
You get what you pay for, and all that.