Gabriel Villasurda offers a number of free resources for string education. His finger patterns are invaluable for improving intonation in a variety of keys.
Tied to the popular guitar workshops, this site provides practical tips for starting and maintaining a guitar curriculum. The forum is not very active, but does store some good conversations.
Similar to Soundtrap.com; this online DAW is a great resource for student to create music with loops. I've used this in a technology class and students enjoy the variety of loops.
This site contains a number of great ideas for tech integration in the orchestra classroom. The tuning automation idea is good way to use technology to streamline the start of class.