CDO is a large tool set for working on climate and NWP model data. NetCDF 3/4, GRIB 1/2 including SZIP and JPEG compression, EXTRA, SERVICE and IEG are supported as IO-formats. Apart from that CDO can be used to analyse any kind gridded data not related to climate science. CDO has very small memory requirements and can process files larger than the physical memory.
CDO is open source and released under the terms of the GNU General Public License v2 (GPL).