Liblinebreak is free software and the source is available: http://vimgadgets.sourceforge.net/liblinebreak/ .
I don't think it was packaged, though.

I tried to install diablo package, as well as compile it's source on Mer, and the result is almost working, but trying to open the settings dialog results in a hang using 100% CPU.

There is fbreader in ubuntu repository, but it does not support full screen, and does not allow mapping +/- keys for next page/prev page, etc.