ERDAS Foundation 2011 is a full released product that installs common-use large files and utilities. It also includes a copy of the ERDAS-Net License Manager 2011. ERDAS Foundation 2011 is a prerequisite for ERDAS IMAGINE 2011, LPS 2011, ERDAS ER Mapper 2011 and ERDAS APOLLO 2011. For ERDAS APOLLO Essentials - Image Web Server, you are not required to install ERDAS Foundation, but you should do so, as it provides the high-detail datums and other large-file reference data. ERDAS Foundation 2011 includes the ERDAS-Net License Manager 2011, which need not be downloaded separately, unless you are setting up a stand-alone license manager away from your ERDAS workstations.
Note that ERDAS Foundation 2011 is not a runnable product by itself.