1. Paragon Systems’ PTS-DOS (http://www.paragon-gmbh.com/n-dos.htm) – An open-source (but not free) DOS replacement fully compatible to MSDOS 6.22 and Microsoft Windows 3.x. Includes a variety of other nice features missing from MSDOS.(It is not really open source. Only the source code of an old Paragon PTS-DOS Version is available. PhysTechSoft says, the Paragon-Version is illegal, because the source code was stolen by programmers which left PhysTechSoft and founded Paragon).
2. PhysTechSoft DOS (http://www.phystechsoft.com/ptsdos/) –
From the home page:
PTS-DOS is the powerful and fastest DOS with network support, file manager, archiver, internal boot viruses protection and numerous utilities package. Now PTS-DOS pack contains graphical web browser, e-mail client, telnet and ftp client!
the unofficial faq page + DOS wiki (http://www.almnet.de/ptsdos/)
TakeDown.NET -> “PTS-DOS”