In the (not) good old days of single-user single-process MS-DOS TSR programs were a kind of magic wish: have more than one program running at same time.
Companies created TSR utilities. I can remember of Borland Sidekick and Norton Guides, among others.
Of course I couldn't leave behind. Around 1990 I created my own TSR program: TASCII. An ASCII table very useful for... me only.
I based my implementation on the excellent Al Stevens' Extending Turbo C Professional book.
Recently I attempted, just for the fun, to bring back TASCII to life again.
I began with the DOSBOX MS-DOS emulator. For the compiler I used Turbo C 2.01 which Borland (now Embarcadero) made available for free, years ago. Unfortunately I hadn't the full source code for the Extending.. book. So I had to borrow it from openlibrary.org and type the missing parts.
Well, here it is (for the real nostalgia DOSBOX has a CGA mode):
Who needs a resident ASCII table these days? But it is nice to see an old friend again.
(If you are also insane I can provide you with the binary).