Here are files you might look into for examples of frequently needed code fragments, or for packages people keep asking about:

• Interrupt-driven serial communications:
  • serial.c in the fsdbXXX.zip package
  • download the aeasy102.zip serial communications package
• Interrupt-driven support of peripheral devices:
  • download the Sound Blaster support package sb02.zip
• Multitasking:
  • download aetsk102.zip
• Port of curses library to djgpp:
  • download pdcursXXX.zip
• X library:
  • Xlibemu is available as xlib03sr.zip by anon ftp from omnigate.clarkson.edu:/pub/msdos/djgpp/pub and also from asterix.inescn.pt
  • Xlib and Xt for DV/X are available from where you got djgpp (get the files qddvxNNN.zip, qdlibNNN.zip and qdtktNNN.zip)