Pre-Boot Software
Boot Managers
GAG
GAG 4.9 (download URL #1), GAG 4.9 (download URL #2), GAG Español Zip: Instructions translated to Spanish, GAG Español Zip: Additional download mirrors, Local directory (with renamed files)
[#xfdisk]: XFdisk (eXtended FDisk)

XFdisk 0.9.3 Beta EN, XFDisk 0.9.3 Source Code (by the later developer, Ulrich Müller), XFDisk 0.9.3 source code (renamed from xfd_325.zip), XFDisk 0.7.0 beta's source code (version by original author Florian Painke), Wayback machine's copy of XFdisk logo. Also the main XFdisk page distributed: xfd093de.zip (Deutsch, German), xfd093nl.zip (Nederlands, Netherlands), bp7crt.zip (needed for the partition manager to work on faster computer). (I have made arcxfd.htm from Wayback machine copy of XFdisk home page (Wayback machine version of German version of page) I also have the foreign language versions in TOOGAM's XFdisk directory, which were obtained from http://www.mecronome.de/xfdisk/files/. while they were available there. (The history_en.txt file from that site is the same as the HISTORY.TXT file in xfd093en.zip.) (For more information about the Borland/Turbo Pascal issue, official statement, Fix for "Runtime Error 200" bug of Borland Turbo Pascal 7 on fast PCs, TOOGAM's section on Runtime 200.)

XFDisk is used as part of the FreeDOS installation process. It is part of FreeDOS's fdbasecd.iso and can be obtained from ibiblio's site for FreeDOS disk utilities (via HTTP) and ibiblio's site for FreeDOS disk utilities (via FTP).

Ranish Partition Manager
Ranish Paritition Manager 2.44 Beta-Beta-Beta, Ranish Partition Manager 2.37 (runs on 8086), Ranish Partition Manager 2.40 (version labeled "stable", by Mikhail Ranish), Ranish Parition Manager 2.43 by Muthu
GRUB
Erikc Boleyn's GRand Unified Bootloader refers to the subsequent product GNU GRUB. GRUB4DOS hyperlinks page has a hyperlink to grub4dos project page. These pages also host WINGRUB. “GRUB for DOS” on freshmeat describes versions, GRUB for DOS tutorial shows usage
Windows NT boot manager
I am not aware of this being a free download. Q157992: How to Triple Boot to Windows NT, Windows 95/98, and MS-DOS. It involves saving the desired boot sector to a file and having boot.ini refer to the file.
Partition Modifiers
FDisk (Fixed Disk)
FDisk programs w/ boot managers
XFdisk, listed on the boot managers section of this page, contains boot manager that is installable in DOS. Ranish Partition Manager also has a boot manager. These files are in the Boot Managers section (earlier on this page).
Free FDISK: The official FDISK of FreeDOS
Free FDisk 1.3.0 Beta/Debug FDisk 1.3.0 (source), Free FDisk 1.2.1
Microsoft's FDisk
Q263044 (English) (renamed locally to 263044u8.exe) to make disks bigger than 64MB work as long as they are also not larger than about 127.5GB. (That is limit of 28-bit LBA, after which point LBA48 is needed. There may also be a limit caused by FDisk's memory allocation.) Large disks may cause severe cosmetic issues (where data overflows one field and causes later fields to have extra text, causing major alignment issues with what is displayed on the screen). (This Windows executable can be viewed using 7-Zip for Windows.)
Other partition modifiers
Hard drive imaging software
Ghost, etc.