It's better to start a new topic and to use the SRT (https://www.phpbb.com/support/srt/) so that suggestions (or answers) are relevant to your situation.
Spelling is freeware, which means you can use it for free.
On the other hand, it is not open source, which means you cannot change it or publish it in a modified form.
Time flies like an arrow, but fruit flies like a banana.