This is the official development repository for BCFtools. It contains all the vcf* commands which previously lived in the htslib repository (such as vcfcheck, vcfmerge, vcfisec, etc.) and the samtools BCF calling from bcftools subdirectory of samtools.
For a full documentation, see bcftools GitHub page.
Other useful links:
File format specifications live on HTS-spec GitHub page htslib samtools tabix