updated: June 11, 2010

BIOS/CMOS

 WipeCMOS [1k] + Clears all CMOS settings to recover from lost passwords or corrupt BIOS settings.

 BIOS [24k] + Saves and restores BIOS settings

OSs, Boot Disks, etc

 QNX Demo Disk [1400k] + "A Web browser, a web server, a POSIX-certified realtime OS, TCP/IP and a windowing system on a single 1.44 Mbyte floppy disk." (Note: QNX has removed the Demo Disk from their website and has not responded to my phone calls and emails to restore it or allow me to post it here. The link, therefore, points to the Wayback Machine's cached version. You can find the downloads here.)  

 MENUET OS [1420k] {S}+ "An OS written fully in 32 bit assembly. It's a Real-Time, graphical OS for 32 bit asm programming, and it fits on a single floppy."  

 KolibriOS 0.7.7.0 [1440k] {S}+ A small x86 assembler hobby operating system, forked from MenuetOS in 2004.  

 Visopsys 0.69 [1440k] {S}+ A fully multitasking, 100% protected mode, virtual-memory, massively-monolithic-style kernel with a bare-bones C library and minimal suite of applications.  

 colorForth [63k] {S}+ An OS, development system, and language rolled into one.  

 FREESCO [1330k] {S}+ Router with many features of a full OS. Easy to setup and can be run off a single floppy.

The Ultimate Boot Disk 4.3m [615k] + Partial list of features: Restores system files, installs Windows faster, identifies PC hardware, extracts Windows cd files, troubleshoots startup errors, clones drives or partitions, streamlines the registry, optional virus scanner.

 Bart's Network Boot Disk [390k] + Network boot disk with PCI NIC auto-detect, support for TCP/IP, Nwlink and Netbeui, over 100 driver plugins available.  

The BootDisk Project & Bootdisk.info provide a wide variety of bootdisk images.

Unix, GNU, etc

Explore2fs 1.07 [384k] {S}+ GUI explorer tool for accessing ext2 and ext3 filesystems.  

 Berkely Utilities [819k] + A set of 40 UNIX-like utilities for MS-DOS, each around 20k. Formerly $200, now free. Includes: awk, basename, cal, cat, cb, cmp, comm, cp, cut, df, diff, dtree, du, ech, ed, expand, find, grep, head, join, ls, make, more, mv, od, opts, paste, rederr, rm, sed, sort, split, tail, tee, touch, tr, unexpand, uniq, wc, which, xstr.

 Swiss File Knife File Tree Processor [1096k] + A veritable treasure chest of functionality bundled up into a single EXE: grep, tree size list, instant FTP/HTTP server, text line filter, text replace, duplicate file finder, split/join files, create MD5 lists, run command on many files, extract strings, and much more.  

 Unix Tools [1166k] + 17 Unix utilities that execute from one EXE without ever extracting to disk. Includes: Bash, Less, Gzip, Grep, Find, Df, Du, Ls, Cat, Cp, Mv, Ps, Rmdir, Mkdir, Rm, Pwd, Tar.

Cygwin-Lite [1280k] {S} UNIX-like command-line environment for Win9x/Me/NT4/2000

 GNU utilities for Win32 [1454k] {S}+ Over 100 GNU apps ported to native Win32 (see this post for more information).   

GNUWin32 [various sizes] {S}+ Over 150 GNU apps ported to native Win32.  

Google's listing of floppy-sized Linux distros

Macintosh

 Gemulator Explorer [30k] + "Access and copy files from any Macintosh 1.44M floppy disk, Macintosh CD-ROM, Macintosh ZIP disk, external Macintosh SCSI hard drive, Atari ST formatted floppy disk, Atari ST ZIP disk, Atari ST formatted hard drive, and even disk image files."  

HFVExplorer [405k] + Access Mac disks under Windows  

Registry, Cleaning, & Tweaking

 Regcmd 0.88a [25k] Command line based Registry editor.   

 RegShot v1.7.2 [28k] {S}+ Uncover registry changes   

Tweak UI 1.33 [64k] Tweaks for the Windows User Interface  

Regmon [72k] {S}+ Monitors and displays all Registry activity  

Test-Run 2.1.0 [136k] Protects the registry while testing new software.

 RegSeeker [242k] + Powerful registry cleaner and more. Free for personal use.  

98lite [349k] $ Remove web integration and many other resource-hogging "features" from Windows 98/Me.

RegCleaner [540k] "Easily get rid of those old and obsolete registry entries created by software that you have destroyed ages ago."  

Startup Managers

StartupRun v1.20 [27k] + A better msconfig.  

 A-spy 0.0.9 [318k] + Startup manager with an "About" box which provides scads of live system info.  

Process Monitoring & Terminating

 AppSwat v1.3.0.0 [8k] + Process terminator. Command-line termination, system startup integration and an effective termination mechanism.  

Procmon [33k] {S}+ View, terminate, and prioritize active processes  

 ProcX 1.000 [55k] + Light yet powerful task manager.  

PrcView 3.7.2.5 [92k] + Process viewer/killer. Includes both GUI & CLI versions.

Process Explorer [230k] + Process viewer/killer. Displays process icon, command-line, full image path, memory statistics, user account, security attributes, DLLs. Also includes search function.  

System Info & Diagnostics

 Uptime [6k] + Displays uptime in console

 UpTime 1.0 [13k] + Displays up-time in a tooltip from the system tray  

 MemTest 3.8 [15k] + RAM reliability tester that runs under Windows.  

 CPU Info [17k] + Determines CPU type, vendor, serial number, and clocks CPU speed.

 Infoman2 [20k] + Tiny display of available free physical memory and system resource data.   

 MyCPU 1.13f [47k] + Displays CPU info: vendor, type, model, stepping, speed, cache, more.  

 Memtest86 3.0 [51k] {S}+ A thorough, stand alone memory test for x86 architecture computers.

MBProbe 1.31 beta 9 [69k] + Monitors voltages, temperatures and fan speeds using hardware monitoring chip(s) available on many modern motherboards. (Download also includes contents of MBProbeNT.zip: giveio.sys and ntinst.exe)   

 TinyResMeter [92k] + System resource information tool  

 SpinRite 5 [95k] $+ "The most capable, thorough, and reliable utility that has ever been created for the long term maintenance, recovery, and repair of mass storage systems."  

 WinAudit v1.2.2 [112k] + System info tool that lists: installed software, license information, peripherals, memory usage, processor model, network settings and more. Reports can be saved in several file formats.  

 HD Tune [131k] + Hard disk utility which reports drive info, health, and benchmarks.

 PCI [164k] {S}+ Produces detailed report of all connected PCI, AGP & CardBus devices, including the system chipset.

 CPU-Z 1.30 [296k] + Displays CPU, Motherboard, Memory, and System info.  

 Unknown Devices [392k] {S}+ Determine the identity of unknown devices in Device Manager.  

 NSSI [397k] + Hardware information tool with many advanced features

Belarc Advisor [565k] "Generates an HTML profile of everything installed on your computer, from your main circuit board to software. Version, manufacturer, and serial numbers are listed, as well as statistics such as available memory slots and hard drive space." Free for personal use.

 PCISniffer 1.2 [675k] + Bootable floppy that detects and displays all PCI busses and devices. Database includes approx. 4000 devices and 1500 vendors.  

 AIDA16 [1054k] + System information program. Extracts details of all components of the PC. Can display information on the screen or write it to file.  

Other

 DDL [4k] + Load DOS device drivers from the command line, without having to reboot.  

 XMSDSK & EMSDSK [75k] + A RAM disk which can be created, resized, and destroyed from the command line  

Filemon [76k] {S}+ Monitors and displays file system activity in real-time  

Virtual Disk Driver (VDK) 3.2 [100k] {S}+ Mount VMWare virtual disks and raw sector images (made with tools like ddrescue) under 32-bit versions of Windows NT/2000/XP/2003.

 Boot Log Analyzer [234k] + BOOTLOG.TXT filter  

 OllyDbg v1.10 [1085k] + 32-bit assembler-level analyzing debugger for Microsoft Windows with intuitive interface. Emphasis on binary code analysis makes it particularly useful in cases where source is unavailable. It predicts contents of registers, recognizes procedures, API calls, switches, tables, constants and strings, locates routines from object files and libraries, allows custom labels and comments in disassembled code, writes patches back to executable file and more.