From NCH Software:
Free music notation and composition software to arrange your own professional quality sheet music using a wide array of music symbols and notes. Crescendo Music Notation Editor features: Change the key signature and time signature. Add whole, half, quarter, eighth and sixteenth notes and rests (semibreve to semiquaver). Compose music in Treble, Bass or C Clefs (e.g., Alto and Tenor). Assign sharp, flat and natural accidentals to notes. Keyboard shortcuts toggle between notes and rests. Insert text to specify a title, tempo, dynamics or lyrics. Drag notes to change their pitch or placement. Automatically detects if a measure has the correct beat amount for the time signature. Adjust staff line placement by snapping them to margins or other staff lines. Add ties and slurs across notes. Zoom in and out for easier editing. View history of work completed. Save to Crescendo's format, or export as MusicXML. Print completed music projects, or blank music sheets for hand transcription. Create dotted notes, chords, add repeats.
It's free! And it's really easy to use. Key changes are easy, though you have to change each line separately. Basic commands are easy to use. The best thing I used i for was a write a hymn. By expanding the staves, it accommodates multiple lines of text between the music, which is something more expensive programs don't do.
Key change isn't universal - it's line by line. I can't find a way to insert double bars to end the song. It would be great if the notes and key signatures all changed with a key change. As it is, you have to change each line's key signature and each note individually.
In the newer versions you can now choose if key signatures change the notes or leave them the same to change sound of the notes. Applying a key change on a bar will also change all of the following bars that have the same key.