Since Abraham, the original Oral Torah allegedly consisted of the currently known 6 Sdarim (although the number of Masechtot was much bigger, up to 6000?).
The Mishnah and naturally the Talmud are also arranged by the Sdarim. The interpreters of the Talmud also followed that order and wrote their notes alongside the Talmud.
Who was the first to write a stand-alone Halachic compendium (not a שו"ת) that did not follow the Mishnaic order (Berachot, Moed etc), "inventing" an order of its own (or was it Rambam's היד החזקה)?
NB: As I've checked, it seems that the books הלכות פסוקות and הלכות גדולות both follow the Mishnaic order (by the Seder of the Talmud).