Obviously there are issues with file IO and permanence when you work within the confines of a browser, but there are hacks around that. And this is a purely visualization tool. Only simple analysis like filtering by gene expression, blast, go data are available. You'd be surprised at how fast browsers are for rendering large amounts of data.
So far I've implemented a genome browser that works pretty much exactly like IGV and an expression data viewer for the dataset my lab uses. It works purely on the client side without a server. So you could just load it on a USB stick and have it work on any relatively new Chrome/Firefox/Safari browser without any dependencies.
I've also made it python compilable. So you just have to input some fasta,tab delimited, gtf files into a python script, and it will generate all the necessary html/js files. It is still very much a work in progress.
Here is a screenshot of the app: