UPDATES:
Version 1.4.2 (Jan 1 2024): Rotational tweening feature now available to complement linear, both options found by clicking the 'tween' button.  Rotational tweening maintains total stroke length despite severe changes in stroke angle to avoid foreshortening.
Version 1.4.1 (Nov 25 2023): Bug fix for max frame inconsistency on playback
Version 1.3.12 (Dec 27 2022): Memory leak fix for fill shapes
Version 1.3.1 (Dec 12 2022): Ability to draw and tween/interpolate solid, filled shapes
Version 1.3.0 (June 4 2022): New canvas drawing toolpicker with improved palette and stroke width customization in addition to smaller design changes.
Version 1.1.41 (March 14 2022): Stability improvement for sequence of touch events preceding a non-drag frame copy and color changes affecting older versions of iOS 14.
Version 1.1.3 (Dec 26 2021):  Apologies to iOS 15 users who experienced crashes when selecting the eraser tool.  The issue was caused by inconsistency in how iOS 14 vs iOS 15 treat changes in selected canvas tools.   We apologize for problems in such fundamental functionality.  Version 1.1.3 includes a fix on tested devices iPad Air 2020, iPad 5Gen, and more recent iPad Pros.  Please email autotween-support@protonmail.com if the problem persists.
Version 1.1.2 (Oct 28 2021): Fix for crashes due to deleting all animation projects.