The ScreenSteps desktop editor has spell check built in. You can either check spelling as a one-time event, or you can check spelling as you type.
On macOS the language that is being spell checked will be determined automatically. On Windows you can select from one of the pre-installed spell check dictionaries.
You can also turn on spellcheck so that it checks spelling as you type, and underlines misspelled words.
Click Edit > Spelling > Check Spelling While Typing.