It's time to start controlling the galaxy, and the best tool for the job is a self-replicating probe. Space probes that can go incredibly long distances, replicate themselves, and carry things like surveillance devices or molecular foundries, are the brainchild of mid-twentieth century futurist John Von Neumann. Often called Von Neumann Probes, his invention fuels both science fiction and real-life plans for space colonization. In some ways, the Voyager spacecraft are crude, nonreplicating Von Neumann probes, hurtling through space in the hope of making contact with another civilization. Over at Sentient Developments, George Dvorsky has written a great essay on the seven best ways to control the galaxy with Von Neumann Probes.
Dvorsky points out that there are nice things you can do with probes, like using them for communication as in the Bracewell Probe model. Says Dvorsky:
Christopher Rose, an electrical engineer at Rutger's University, has suggested that we should actually look for these probes in our own Solar System. He argues we should be checking the mail instead of waiting for a phone call.
Multiple Bracewell probes could also be set up as a distributed array of communication relay stations. Such a set-up was portrayed in Carl Sagan's Contact. In this story, a dormant Bracewell probe was lying in wait in the Vega system. It began to transmit a strong signal after it received a radio signal from Earth. The device itself was part of a larger network of probes, as witnessed later by Ellie's journey from probe to probe.
If we are going to embark on megascale engineering projects, we're going to need robots. Lots of 'em. Projects like Dyson Spheres, Ringworlds and Alderson Disks would require fleets of specialized and artificially intelligent probes working in concert to construct these truly massive structures.
Probably the most truly hardcore probe is the Berserker probe, sort of an anti-terraforming device, used to spread death and destruction across the galaxy:
Berserkers could be disseminated with the sole purpose of sterilizing every planetary system it encounters, forever eliminating the possibility for life to emerge and evolve. Should it encounter an inhabited planet, it could use any number of schemes, including nanotech instigated ecophagy, to quickly destroy all life in a matter of hours. By using a scorched galaxy policy, a civilization could sterilize the Milky Way in about 500,000 years.
Alternately, berserker probes could be disbursed across the entire Galaxy and lie dormant, patiently waiting for signs of intelligence.
Seven Ways to Control the Galaxy with Self-Replicating Probes [Sentient Developments]