eComStation by Serenity Systems and Arca Noae
the king is dead. long live the king.
everyone seems to be talking about OS/2 as though it is dead. it certainly isn't and many people still use it today.
Serenity Systems created eComStation which runs on modern hardware and was originally based on OS/2 Warp Version 4. It's still in full production today.
http://www.ecomstation.com/
and then we also have Arca Noae https://www.arcanoae.com/ which is due for release soon.
Warpstock still runs events annually http://www.warpstock.org/
many people still run this platform and some developers still release applications for it as well. there is a massive archive on Hobbes http://hobbes.nmsu.edu/ and also OS/2Site http://www.os2site.com/
software such as Weasel http://pmoylan.org/pages/os2/Weasel.html which is a fully featured mail server is still being actively developed as of right now :-)
cheers, wizdude