On older stuff it's hard to separate paid-and-now-free from always-free.... but among the things that were definitely free, no doubt about the top ones.

Rikugame's "Kona" figure has been the main character in my blog for 9 years, and she's been joined recently by MrSparky's Danbo figure.  (Both are somewhat modified and re-rigged.)

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My ShareCG freebies