Windows 2000 has been unsupported by Microsoft in 2009 after four service packs and one update rollup. While it has been put out of service by many, it is still a very popular OS for those running virtual machines (VMs). Its RAM requirements are fairly low and the OS is quite speedy.
However, many developers do not support Windows 2000 anymore, whether explicitly or simply by ignorance. There
are were issues with recent versions of VirtualBox VM Guest Additions.
SumatraPDF supports Windows 2000 up to Version 1.6. Later versions refuse to start due to being compiled with VS 2010.
Deutsche Bahn’s timetable still supports Windows 2000 in its latest incarnation (2013). So does VBB-Fahrinfo offline.
Avantix Traveller still supports Windows 2000.
7-zip also still supports Windows 2000.
The last Microsoft Office version to support Windows 2000 officially is Office 2003.