Wallace Inline was a WordPress plugin developed by Bradley Kirby from 2017 to 2021. It is no longer under development. Below you can find a free download link and source code access.
Download: https://www.dropbox.com/s/7qdlnhjtf0u4dlz/wallace-inline-2.2.18.zip?dl=0
Git: https://bitbucket.org/bkirby/wallace2/src/master/