I like old tech. Really old tech and really old software.

WinWorld maintains a library of original install media for tons of really great and otherwise hard to find abandonware operating systems and programs for DOS and Windows 3.1, etc.

BBS software for DOS at Jason Scott’s BBS Documentary site:
PCBoard by Clark Development Software
WildCat! by Mustang Software Inc

 

Virtualization and Emulation
VirtualBox – virtualization hypervisor
VMware Player – virtualization hypervisor
DosDox – MS/PC-DOS emulator
PearPC – PowerPC architecture emulator
Virtual PC 2007 SP1 – virtualization hypervison
QEMU – processor emulator
bochs – x86 PC emulator

Archive and Disk/Disc Image Manipulation
UltraISO – CD/DVD imaging tool
WinISO – CD/DVD imaging tool
WinImage – floppy disk imaging tool
7-Zip – archiver

Drivers
S3 Trio64V+ legacy driver (for DosBox)
Sound Blaster 16 legacy driver

 

Old Linuces
RedHat Linux 6.2 at Red Hat’s download archive (up to 9.0 available).
SuSE Linux 9.3 (Direct) or here at the Internet Archive