Let's think on this statement a little. From top of my head:
- VLC
- Darktable
- rsync
- KDE as in the Desktop Environment
- Clementine Music Player
- MusicBrainz Picard
- GIMP
- Zotero
- GNU Octave
- Kid3
- KMail
- etc, etc...These apps are not sponsored by corporations directly.
Also, your point is untenable. The moment someone patches something while being employed by a company, that thing becomes "developed via corporate paycheck". This also makes the small tools developed by oneself "developed via corporate paycheck", because while the person was at home, and it was 2AM, They also had a job paying their bills somehow.