OS2LDR
OS2LDR is known as the OS/2 Loader.
OS2LDR module, running in real mode, sets up the PIC chips, sets the PIT timer chips, queries the BIOS for hardware configuration data, reads various CMOS and ROM information, and finally loads (i.e., reads in and applies fixups to) OS2KRNL and transfers control to it at its start address, syiInitializeOS2.
Alternative Version
QSINIT
There is a OS2LDR alternative called QSINIT which is a OS2LDR replacement made form scratch and gives more functionality to the regular OS/2 loader. Currently it is freeware for non-commercial use and the source code is also available.
FreeLDR
FreeLDR is a project created by David C. Zimmerli to create a replacement loader for OS/2. The source code was posted in conjunction with the "A Project to Replace OS2LDR" article.