Cosoxword is the program that I use to help me solve crosswords. I wrote it years ago and it only works on computers, NOT on phones or tablets. It's free but does require Java to be installed. Windows and Linux require Java 8 or above. Mac requires Java 9 or above.

There's a page of screenshots here.

Linux download: cos.tar.gz

Mac download: cos.dmg.xz

Windows download: cos.zip

If you're interested in quizzes, there's also TrivKey.