I think introducing web-based content in a high school math course (or any level math course, for that matter) demands a lot of work for little to no return. I understand that you want to engage your students, but I think that trying to do so in a web- or computer-based environment will lead to them spending more time battling the interface than solving or thinking about problems. Just think about the amount of time it took you to learn Latex when starting out.
If you want to get your students to think about math, and talk about math between themselves, then find good, instructive problems for them to solve. Preferably ones that can be expressed in some real world or simple geometric terms, and that can be visualized or drawn. Visual aids are your friend. Rubics cubes, bits of string, pieces of paper - whatever you can find to bring your problem to life is helpful.
Then put them into a long, coherent problem sheet with a clearly identifiable result at the end, and assign it as a group project. Give them a week, have them work in groups of three or four on the problems, and make them hand it in as a team. At the end, get one or two teams to present their work to the class. Try and get the class to discuss the solutions. Then change up the groups and repeat.
Of course this demands an incredible amount of work from you as a teacher. But it'll be work put towards teaching your students mathematics, instead of teaching them to claw their way through a halfway functional web interface.