I suggest the following :
1) Web App(Client side) : AngularJs since this library probably be useful (https://github.com/angular-gantt/angular-gantt) and others. An alternative would be node.js
2) For the server-side you can do Django(in python), in C++(using cppcms) or even better in Exilir/Erlang(Somehow difficult but much better option in my opinion).
3) For the webapps its pretty much straight forward (android/iOS)
I would go with any extensible technology. because we are to build on it (Make more additions with time) .So its fine with the suggestions. So client tech is fine....and C++ is also fine. but we could try Erlang..
I suggest the following : 1) Web App(Client side) : AngularJs since this library probably be useful (https://github.com/angular-gantt/angular-gantt) and others. An alternative would be node.js 2) For the server-side you can do Django(in python), in C++(using cppcms) or even better in Exilir/Erlang(Somehow difficult but much better option in my opinion). 3) For the webapps its pretty much straight forward (android/iOS)