Yes, bash!
At least, I am with the mass
Btw. everybody use it in most linuxes, even if that's not a login shell
For example on debian (file's output in /bin):
/bin/gunzip: Bourne-Again shell script, ASCII text executable
/bin/gzexe: Bourne-Again shell script, ASCII text executable
/bin/uncompress: Bourne-Again shell script, ASCII text executable
/bin/zcat: Bourne-Again shell script, ASCII text executable
/bin/zcmp: Bourne-Again shell script, ASCII text executable
/bin/zdiff: Bourne-Again shell script, ASCII text executable
/bin/zegrep: Bourne-Again shell script, ASCII text executable
/bin/zfgrep: Bourne-Again shell script, ASCII text executable
/bin/zforce: Bourne-Again shell script, ASCII text executable
/bin/zgrep: Bourne-Again shell script, ASCII text executable
/bin/zless: Bourne-Again shell script, ASCII text executable
/bin/zmore: Bourne-Again shell script, ASCII text executable
/bin/znew: Bourne-Again shell script, ASCII text executable
And in /usr/bin there is much more, for example ldd, tzselect...
But hey, the /sbin/dhclient-script, and the so old /usr/sbin/mkrescue is in bash
I always wondered that why they are not "simple" posix shell scripts like the which, dvipdf, nrof ... but anyhow I think most of the distros not even provide bash but depending on that now for very common utilities (I won't call them "binaries").