Get a steady beat or an "A" for tuning:
https://www.metronomeonline.com/legacy
Hear any note for tuning: use the drop down menu to the right under the slider to pick the notes you want by letter name. Caution: Do not use this with headphones!
http://plasticity.szynalski.com/tone-generator.htm
Listen to music were are playing in orchestra (make sure you type in the correct arranger), even browse for music:
http://www.jwpepper.com/sheet-music/welcome.jsp
Note reading practice, treble clef:
http://www.classicsforkids.com/games/notename/notename.html
Note reading practice, treble, alto, and bass clef:
http://musicteachersgames.com/linesSpaces
For fun: Chrome Music Lab:
https://musiclab.chromeexperiments.com/Experiments