NoMaps is a standalone tool created by Crytek to achieve high quality tangent-space normal maps for CRYENGINE. In the past when people tried to create tangent-space normal maps for our ENGINE they had to use software which assumed how our renderer accomplished tangent-space. The problem was that no software would know how exactly CRYENGINE rendered tangent-space, hence normal maps were never guaranteed to be completely accurate - or stay compatible between ENGINE revisions/versions. Now with NoMaps Crytek offers a standalone tool which produces tangent-space normal maps directly for CRYENGINE. This software takes the object and its matching object-space normal map and then converts it into a tangent-space normal map that fits its mesh perfectly. In this way NoMaps helps in achieving high quality assets for CRYENGINE, while simplifying previous workflows (only an object-space normal map is required).
A short introduction to the common misconceptions about tangent-space normal maps:
Bake the normal map. It is recommended to use *.sbm files and modified cages if your low-poly is really simplistic.
Export the lowpoly as a *.cgf using the "custom normals" option. Be sure to turn off any modifiers that change vertex normals (edit mesh, edit normals, etc). This *.cgf is just for baking, the final in game mesh can have custom normals disabled. What custom normals do in this case is not only relevant to the vertex normals, rather the RC attempts to re-orient the vertex tangents to facilitate correct shading and allows for mirrored UV's as per Mikkelsen. NOTE: If you have imported your mesh from Maya to 3dsMax at one point in its creation process you should apply an "Edit Poly" modifier on your object to reset vertex normals, then collapse. This has to be done because Maya has different vertex normals than 3dsMax. Alternatively, you can export your mesh as an *.obj from 3dsMax, then re-import it and use this mesh thereafter.