  We present a C++ software package called PhaseTracer for mapping out
cosmological phases, and potential transitions between them, for Standard Model
extensions with any number of scalar fields. PhaseTracer traces the minima of
effective potential as the temperature changes, and then calculates the
critical temperatures, at which the minima are degenerate. PhaseTracer is
constructed with modularity, flexibility and practicality in mind. It is fast
and stable, and can receive potentials provided by other packages such as
FlexibleSUSY. PhaseTracer can be useful analysing cosmological phase
transitions which played an important role in the very early evolution of the
Universe. If they were first order they could generate detectable gravitational
waves and/or trigger electroweak baryogenesis to generate the observed matter
anti-matter asymmetry of the Universe. The code can be obtained from
https://github.com/PhaseTracer/PhaseTracer.
