What are some alternatives?
When comparing TuxGuitar and Simply Piano, you can also consider the following products
MuseScore - 24 Sep 2012 . Design a homepage that captures attention and serves as a good starting point for navigating the website.
Flowkey - The easiest way to learn piano with your iPhone or iPad
Guitar Pro 7 - Create, play and share your tabs
Yousician - An interactive guitar-learning app.
Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Pianu - Learn to play the piano in your browser.