The latest release of the OOMMF software may be retrieved from the OOMMF download page. Each release is available in two formats. The first format is a gzipped tar file containing an archive of all the OOMMF source code. The second format is a .zip compressed archive containing source code and pre-compiled executables for Windows. Each Windows binary distribution is compatible with only a particular sequence of releases of Tcl/Tk. For example, a Windows binary release for Tcl/Tk 8.6.x is compatible with Tcl/Tk 8.6.0, 8.6.1, ....
For the first format, unpack the distribution archive using gunzip and tar:
gunzip -c oommf20a0.tar.gz | tar xvf -
For the other format(s), you will need a utility program to unpack the .zip archive. One utility program which is known to be suitable is UnZip.
Using your utility, unpack the .zip archive, e.g.
unzip oommf20a0_86.zip
For either distribution format, the unpacking sequence creates a subdirectory oommf which contains all the files and directories of the OOMMF distribution. If a subdirectory named oommf already existed (say, from an earlier OOMMF release), then files in the new distribution overwrite those of the same name already on the disk. Some care may be needed in that circumstance to be sure that the resulting mix of files from an old and a new OOMMF distribution combine to create a working set of files.