OpenIFS is based on IFS Cycle 38r1 (operational model introduced December 2012).
IFS Manuals for Cycle 38r1 (PDF)
The PDF manuals are also available for download (together with a web based source code browser) from the OpenIFS ftp site.
IFS manuals for all model cycles
The full list of IFS manuals are available, though not all are relevant for OpenIFS.
Diagnostics
Manuals provided by GmapDoc website (MeteoFrance)
FULLPOS 'In-model' post-processing
DDH 'In-model' budgets on user-defined domains
ECMWF scientific articles of interest
Numerics of physical parameterization,
Beljaars et al, Proceedings of 2004 ECMWF seminar on Advances in Numerical Techniques.