It was written by high school and middle school teachers in the Arlington Central School District and is being used by students in our district. We had good success with it last year, as measured by the amazingly generous June Algebra Regents exam.
Still, there are about 120 lessons and homeworks available on topics ranging from classic algebra (equations, systems, quadratics, rationals) to right triangle trig, to measurement and error. Feel free to download and use these anyway you like, as review or even as a primary text as we do.
I know this has been posted before, but I thought I would give an update in case anyone had missed it before now.
Kirk Weiler Editor-In-Chief of the Arlington Algebra Project