The stable version of Org is 9.4, as of September 2020. See the release notes.

Get it with M-x package-install RET org RET (see Org ELPA).

Or download tar.gz or zip archives.

You can browse the development version from code.orgmode.org or clone the repo:

~$ git clone https://code.orgmode.org/bzg/org-mode.git

Daily snapshots of the development version: tar.gz or zip.