The leaves don't look succulent to me, and if that is correct, it would rule out rain lily. It also doesn't look like any of the grasses commonly called Monkey Grass (various Liriope sp. & Ophiogon sp.), tho, that's the danger in using common names: completely different and unrelated plants may have the same common name depending on where you live. I think those species generally have a little more substance/thickness to their leaves (tho not quite succulent), while the grass pictured appears to be really thin (not in width, but in cross section).
This one may be some variety of Paspalum species? Just a guess. May have to wait till you see seed heads to get a good ID.