Shameless gentoo plug: gentoo does rolling releases. There's still stable v unstable but it's per-package. I've run everything unstable for years (except the kernel and default gcc which I update only infrequently). Most packages get updated unstable ebuilds within days of release, probably because with nice upstream choices, a new ebuild can be made with a change on a single line. I've even made such an ebuild myself with no experience when I needed today's version.

There's even a way to make an ebuild for nightlies, although you can get build breaks with those.