Relative Notes is a web app for musical training using Solfège, Nashville or Roman numbering. Ear training or learning tunes, for example, work best using one of these relative symbol systems. Each note is given a symbol (Re, 2 or ii) to identify its distance from a tonic note as apposed to using fixed pitch musical note names (D). Then the pitches can be more easily applied in any Key.
Here's a short demo video.
The app monitors MIDI 'noteon' messages coming from external or virtual MIDI devices and displays the appropriate syllable or number. It also shows the notes on an Improvise for Real tonal map diagram as well as some extra detail on the input note.
The original use case was to confirm the relative syllable or number in mind matches what is being played. You can even check what is being sung when used in conjunction with a Pitch to MIDI converter such as Dubler.
Note you will need to enable MIDI access for the browser when asked. In addition, when MIDI devices are connected or virtual midi programs launched the browser will likely need to be refreshed (F5) or restarted in order for them to become available.
When using virtual MIDI devices (programs that generate MIDI) on Windows you might need a virtual MIDI cable such as loopMidi.
This is a Music Practice Tools open source project by Steve Lee for Fullmeasure.uk.