  Let $\Gamma^+$ be the positive cone in a totally ordered abelian group
$\Gamma$, and let $\alpha$ be an action of $\Gamma^+$ by endomorphisms of a
$C^*$-algebra $A$. We consider a new kind of crossed-product $C^*$-algebra
$A\times_\alpha\Gamma^+$, which is generated by a faithful copy of $A$ and a
representation of $\Gamma^+$ as partial isometries. We claim that these crossed
products provide a rich and tractable family of Toeplitz algebras for product
systems of Hilbert bimodules, as recently studied by Fowler, and we illustrate
this by proving detailed structure theorems for actions by forward and backward
shifts.
