> Ah it seems that there is this program called keynav.

Yep, I wrote this as a direct clone of the original keynav, so I can use the same config file on both operating systems.

> For browsers I love to use these pentadactyl/vimium/... extensions. Would there be anything similar for reguar desktop applications. I get that it would be a huge effort to support all the different toolkits though.

You can bind arbitrary keys to control the grid, and the default bindings are vim-like, but it only goes down to the window level. Interesting idea though, probably doable with LD_PRELOAD stuff.