IBM's _(OS/2 Warp | http://www-4.ibm.com/software/os/warp/)
is one branch of what was originally a joint development between
_(Microsoft | http://www.microsoft.com) and
_(IBM | http://www.ibm.com), the other branch being known today as
Microsoft _(Windows NT). It can run most _(DOS) and _(Win 3.x) programs seamlessly, as well as some _(Win9x) software.

While not abandoned by IBM, it is not very actively marketed by them anymore.
However, a company has licensed the right to market an up-to-date _(OEM) version of OS/2: _(eComStation | http://www.ecomstation.com).

Also, OS/2 has long been actively supported by a legion of developer-users and enthusiasts, and good development information is available on the
_(Team OS/2 | http://www.teamos2.org/apps/development.html) and
("Seattle OS/2  users group" | http://www.seaos2.org/refs/develop.html) _(MIA)
sites.

FTP sites for OS/2 software:
_(Hobbes | ftp://hobbes.nmsu.edu), ("FTP-OS/2" | ftp://ftp-os2.cdrom.com) _(MIA)