There  have  been  lots  of  interesting  posts  lately  about  text
formatting tools  [0][1][2][3][4] (I particularly like  the artistic
bent of jynx's  and cat's posts with the embedded  ascii art). Since
I'm an Emacs  guy I've used muse mode  in the past - this  is what I
wrote the SDF Emacs tutorial and  cheatsheet in.  For that they were
invaluable since I had one  source document and could generate HTML,
text, and  epub [5].  Speaking  of formatting,  in Emacs there  is a
minor mode called refill-mode, it auto-fills paragraphs as you type,
with whatever justification you set ('M-x set-justification-full' is
what I'm using for this post).  You can also disable refill-mode and
just manually fill paragraphs with M-q every so often.

[0] gopher://sdf.org/0/users/cat/phlog/fs20180215.txt
[1] gopher://sdf.org:70/0/users/kvothe/phlog/2018/02/07-text-formatting-is-beautiful
[2] gopher://sdf.org/0/users/dbucklin/posts/gopher_groff.txt
[3] gopher://sdf.org/0/users/jynx/dat/20180304.post
[4] gopher://alexschroeder.ch/02018-03-05_Troff
[5] gopher://sdf.org/1/users/slugmax/docs/emacs