I'm currently working on a web tracker, and it turns out that it is /much/ easier said than done. You have all the problems of making a web app, coupled with all the problems of making a tracker (of which there are many). Plus, you seem to be suggesting a one-stop allgear tracker, which makes it ten times worse, since one doesn't seem to exist even for desktop yet.
And, a shoutout to, IMO, one of the coolest quasi-demoscene places on the internet, http://battleofthebits.org. Without them, I would never have gotten my feet off the ground with coding.
And, if anyone's curious (it's still in its incredibly early stages), https://github.com/ianremsen/lunartracker