I am not sure what mdk,fdk actually mean? what do they contain?
These are either foundry/fab dedicated or CAD-company dedicated design kits:
Foundry/fab dedicated design kits contain schematics, symbols, abstracts, perhaps layouts, and simulation models of
their devices (Rs, Cs, diodes, various transistors, and perhaps higher integrated circuits). The general name for these design kits is PDK, but sometimes also more abbreviated names are used, as TDK for TSMC PDK, or UDK for a UMC kit. Usually they are free - for a registered customer, who has to sign an NDA (and hopefully will order many wafer lots of his developed circuit(s) built with their devices).
CAD-company dedicated design kits are provided by the CAD-companies themselves; they contain
their (dedicated) CAD-software for schematic entry with electrical rules' check (ERC), preLayout simulation with general device models (for a specific process size). Until here, this software is
free for education purpose
for Universities and High Schools (which teach Circuit Design), and so for their
registered students - certainly with limited license count.
For real circuit design with production intention, a foundry/fab dedicated PDK (with
their models) now is necessary: the (also) dedicated software for layout, design rules' check (DRC), parasitics extraction, backannotation into the netlist (and perhaps into schematic, too) and postLayout simulation, then layout processing (streaming) into (mostly) GDSII format, possibly back-streaming into a layout netlist for comparison purpose. GDSII is the suitable layout format as
Tape-to-Fab for chip fabrication.
Now all this CAD software is free for download (for registered persons, at the CAD-company and at the foundry/fab) - just the CAD software needs a license - and this costs (a lot of) bucks ;-)
Examples are CDK for Cādence Design Kit, MDK for Mentor, TDK for Tanner (note the abbreviations' accordance with the fap/foundry design kit mentioned above).