Back in April, 1991, Al Stevens started a project in Dr Dobbs called D-Flat
, meant to be a C equivalent for the C++ Turbo Vision around at that time (among others).
Here's an image of it in action, running the MemoPad
application that was included as an example of what it could do:

And another, from an earlier version but showing more control types:

The series of articles ran all the way through to October 1992, when he started work on D-Flat++
. From that first "C Programming" column in April, this is the (abridged) announcement:
My excursion into event-driven programming and my analysis of TurboVision, Zinc, and Mewel, led me to a conclusion. C programmers need an efficient way to put the IBM Systems Application Architecture (SAA) Common User Access (CUA) into their DOS text-mode programs and into programs developed for other, non-PC platforms.
If TurboVision, a lovely new part of Turbo Pascal 6.0, finds its way into Turbo C, it will no doubt be a C++ additive because of its strong orientation to classes. Users of the C component of Turbo C++, Turbo C 2.0, or other C compilers will not benefit from TurboVision.
The Zinc library is likewise a Turbo C++ product. Mewel is a good solution for C programmers, but only if you are developing for the high-end computers, ones fast enough and with enough memory to support Mewel programs, and only if you want most of the features supported by the Windows CUA interface.
Over the next several months I will be publishing a new "C Programming" column project, which will be a C library that implements a subset of CUA in a text-mode environment.
D-Flat will provide the CUA interface in an event-driven architecture with the hardware drivers developed separately. It will support applications windows, child document windows, menu bars, pop down menus, dialog boxes, buttons, edit boxes, list boxes, scroll bars, context-sensitive help, and other CUA things. It will use the C compiler's preprocessor as a resource compiler. The version published here will run on the PC and will compile with as many popular compilers as I can possibly address within the confines of this column and the time I have to give to it. The hardware-dependent and compiler-dependent code will be separate from the rest of the library, and it will be small in relation to the rest of D-Flat.
As you can see, it also mentions a couple of other possibilities if D-Flat is not to your liking.
It appears to have been made available on Github but, even if that disappears, you can probably find it by searching around for dflat20.zip
.
The ZIP package has make files for Watcom, Borland, and Microsoft, and the README.DOC
file contains the following snippet if you're concerned about licensing issues (my emphasis):
The source files in the DFLAT archive constitute the D-Flat windowing
system. This is public domain code. You may use it in your
applications without restriction. You may freely distribute source
code. It would be nice if you would give credit to Dr. Dobb's Journal
as the original publisher of the source code.
Our colleague here, ssokolow, has graciously collected various DFlat packages and put them up on archive.org for easier accessibility.