Xerte toolkits is a powerful free tool with which you can create interactive, mobile-friendly content with high accessibility. However, it needs to be installed on your server by someone with technical skills before ordinary teaching staff can use it.
Xerte has long enjoyed a reputation for creating accessible content but now the drop down colour, font buttons and speech buttons have disappeared some people ask "Is it less accessible than it was". It's actually much more accessible than before (as explained below) but for the worriers there is good news..