Application Software
DOS SFN Family
Programming Tools
IBM Technical Reference = an archive of hard to find DOS programming information (mostly IBM technical document scans in long-filename PDF format).
MS-DOS Programmers Reference = an archive containing the Microsoft MS-DOS Programmers Reference (in nine text files).
Ralph Browns Interrupt List, version 61 = an archive containing details on the useage of all 256 Software Interrupts; plus info on Ports, CPU opcodes, and more.