I've never used InqScribe nor any other subtitle tool, but alternativeto.net has a list of alternatives like Kainote or SubtitleEdit: https://alternativeto.net/software/kainote/?license=opensource There's even a short Wikipedia article: https://en.m.wikipedia.org/wiki/Comparison_of_subtitle_editors

That's what I've been using for a few years now, with SimpleCalendar (soon Fossify) on my phone. Didn't have any problems yet.

Der Krüppel kostet ganz bestimmt nichts für kommerziellen Gebrauch, das würde der Definition von Offener Soße/Freier Weichware widersprechen.