The GNOME project considers gspell to be a superior alternative to gtkspell.

On the other hand, it looks like gtkspell3 is still alive since there
was a new release in September after 2 years of inactivity.

I count about 15 packages using gtkspell3. If these can be ported to
gspell, there won't be a need to keep gtkspell3 around any more.

https://bugs.debian.org/cgi-bin/pkgreport.cgi?users=pkg-gnome-maintainers@lists.alioth.debian.org;tag=gtkspell

References
---------------
https://wiki.gnome.org/Projects/gspell
https://wiki.gnome.org/Projects/gspell/FAQ
https://developer.gnome.org/gspell/stable/

Thanks,
Jeremy Bicha