If you would like to contribute CODE to piano booster below are some suggestions that you could work on.
0. Adding a current dispaly PBM display please see: #70 this is a really easy change.
1. There is the wip/opengl branch that needs completing at the moment as PB does not work on 4K screens and it also needed for older PC. It upgrads to use QOpenGLWidget instead of the obsolete QGLWidget in QT5. It is fairly obvious what need fixing when you resize the window. Please keep the behaviour and sizes much the same for now.
3. There is a http://piano-booster.2625608.n2.nabble.com/Accuracy-bar-td7572921.html Showing a percentage score at the end of playing a song. Years ago i created GuiHighScoreWindow.ui but that is far as I got . A percentage score could be created from detecting and counting up all the right and wrong notes played. I think the GuiHighScoreWindow.ui should be renamed to something like GuiSkillLevelResults.ui. This is quite a fun task that should not be too hard. Also I already have code to record and then replay the piece of music you just played. Again we would probably start with pencil sketches of the UI
4. A feature to go back to the start of current measure see #292 . But for now please just add a keyboard shortcut. Maybe for now using the '<' and '>' keys. I am thinking about how to change the UI for this idea. I want to keep the UI very simple and uncluttered that children can easily use. You might need to search for looping in the source code. MIDI is not like an audio file. For complicated reasons to skip back two bars you need first rewind to the very beginning and play the midi file at high speed without making any sounds until you reach the right point. This is how the play from bar feature works.
PLEASE let me know before you start any major work so that we can coordinate. Thanks