The $\pi$-Calculus.

The $\pi$-calculus [54,53,14,40] is a small calculus based on name passing interaction, which has grown from CCS. A basic form of its operation can be written down as the following reduction.

$$x(y).P\vert{\overline{x}}{\langle v \rangle}\longrightarrow P{\lbrace {v}/{y}\rbrace}$$

Here a name $v$ is communicated via name $x$ to an input process, resulting in name instantiation. In essence, sending a name means sending a link: as a result, the topology of communication -- who can send to whom -- dynamically changes, just as you pass a URL in an e-mail so that the receiver can obtain an access to a new link.