  (Abridged) Recent molecular surveys have revealed a rich gas organization of
sonic-like fibers in all kind of environments prior to the formation of low-
and high-mass stars. This paper introduces the EMERGE project aiming to
investigate whether complex fiber arrangements could explain the origin of
high-mass stars and clusters. We analyzed the EMERGE Early ALMA Survey
including 7 star-forming regions in Orion (OMC-1/2/3/4 South, L1641N, NGC2023,
and Flame Nebula) homogeneously surveyed in both molecular lines (N$_2$H$^+$
J=1-0, HNC J=1-0, plus HC3N J=10-9) and 3mm-continuum using a combination of
interferometric ALMA mosaics and IRAM-30m single-dish (SD) maps. Based on our
low-resolution (SD) observations, we describe the global properties of our
sample covering a wide range of physical conditions including low-,
intermediate, and high-mass star-forming regions in different evolutionary
stages. Their comparison with ancillary YSO catalogs denotes N$_2$H$^+$ as the
best proxy for the dense, star-forming gas in our targets showing a constant
star formation efficiency and a fast time evolution of <1 Myr. While apparently
clumpy and filamentary in our SD data, all targets show a much more complex
fibrous substructure at the enhanced resolution of our ALMA+IRAM-30m maps. A
large number of filamentary features at sub-parsec scales are clearly
recognized in the high-density gas traced by N$_2$H$^+$ directly connected to
the formation of individual protostars. This complex gas organization appears
to extend further into the more diffuse gas traced by HNC. This paper presents
the EMERGE Early ALMA survey including a first data release of continuum maps
and spectral products for this project to be analysed in future papers of this
series. A first look at these results illustrates the need of advanced data
combination techniques to investigate the intrinsic multi-scale, gas structure
of the ISM.
