The Linkesoft app seems to be called Songbook ChordPro on iOS (the first link - which sometimes fails here) but SongBook on Android and Mac.

As I'm using an Android tablet here I looked in Google Play. There is also a Songbook (no capital B) and SongbookPro (which looks similar) and various other combinations of songs, books, and chords.

Nothing called 'on song' in G-Play, but there is an app called OpenSong - which is free.