People have attempted to make open source lesson planning tools, but the ones I've seen have been low quality. People have attempted to make proprietary tools, but teachers don't have the funds to pay for proprietary planning tools.
I think the education world is ripe for a revolution in open infrastructure. The ed-tech world is seeing a flurry of startup efforts, but many will die out because their goal is to make money. We need high-quality open tools and resources in the profession.
I wrote a longer post about this a while back: https://peak5390.wordpress.com/2012/02/07/why-do-programmers...