  Radio astronomy has traditionally depended on observatories allocating time
to observers for exclusive use of their telescopes. The disadvantage of this
scheme is that the data thus collected is rarely used for other astronomy
applications, and in many cases, is unsuitable. For example, properly
calibrated pulsar search data can, with some reduction, be used for spectral
line surveys. A backend that supports plugging in multiple applications to a
telescope to perform commensal data analysis will vastly increase the science
throughput of the facility. In this paper, we present 'SETIBURST', a robotic,
commensal, realtime multi-science backend for the 305-m Arecibo Telescope. The
system uses the 1.4 GHz, seven-beam Arecibo L-band Feed Array (ALFA) receiver
whenever it is operated. SETIBURST currently supports two applications:
SERENDIP VI, a SETI spectrometer that is conducting a search for signs of
technological life, and ALFABURST, a fast transient search system that is
conducting a survey of fast radio bursts (FRBs). Based on the FRB event rate
and the expected usage of ALFA, we expect 0-5 FRB detections over the coming
year. SETIBURST also provides the option of plugging in more applications. We
outline the motivation for our instrumentation scheme and the scientific
motivation of the two surveys, along with their descriptions and related
discussions.
