• Arca Noae – operating system, based on OS/2 Warp 4.52
• EComstation – the old rehash of OS/2
• EComstation.ru
• OS/2 World – community resource for OS/2
• Netlabs
• Netlabs Wiki
• FreeRTOS – Real-time operating system for microcontrollers
• HAIKU an open source operating system
• FreeDOS

• Software optimization resources
• EDM/2 Wiki – source for OS/2 and eComStation developers
• Open Watcom – Open Source Watcom C/C++ and Fortran cross compilers and tools
• Open Watcom v2 – current Open Watcom source
• kLIBC svn page 
• The un*x to OS/2-EMX Porting FAQ
• The POSIX/2 Project
• Alexander Mai’s OS/2 page
• Paul Smedley’s gcc port page
• AndyMac’s Home (Python port)
• Tavi OS/2 pages
• osFree project – a free OS project
• osDev – OS development site – very good
• Operating Systems Paul at Rutgers Spring 2015

Blogs

• pagetable.com  Some Assembly Required
• Fun with virtualization 
• Bleepingcomputer