  Over the last two decades, following the early developments on
maximally-localized Wannier functions, an ecosystem of electronic-structure
simulation techniques and software leveraging the Wannier representation has
flourished. This environment includes codes to obtain Wannier functions and
interfaces with first-principles simulation software, as well as an increasing
number of related post-processing packages. Wannier functions can be obtained
for isolated or extended systems (both crystalline and disordered), and can be
used to understand chemical bonding, to characterize polarization,
magnetization, and topology, or as an optimal basis set, providing very
accurate interpolations in reciprocal space or large-scale Hamiltonians in real
space. In this review, we summarize the current landscape of techniques,
materials properties and simulation codes based on Wannier functions that have
been made accessible to the research community, and that are now well
integrated into what we term a \emph{Wannier-functions software ecosystem}.
First we introduce the theory and practicalities of Wannier functions, starting
from their broad domains of applicability to advanced minimization methods
using alternative approaches beyond maximal localization. Then we define the
concept of a Wannier ecosystem and its interactions and interoperability with
many quantum engines and post-processing packages. We focus on some of the key
properties that are empowered by such ecosystem\textemdash from band
interpolations and large-scale simulations to electronic transport, Berryology,
topology, electron-phonon couplings, dynamical mean-field theory, embedding,
and Koopmans functionals\textemdash concluding with the current status of
interoperability and automation. The review aims at highlighting basic theory
and concepts behind codes, providing relevant pointers to more in-depth
references.
