Slate
A fast, simple text editor that opens files of any size
...An 800 MB JSON file or log shows up in a fraction of a second and stays smooth to scroll and search, because Slate only reads and draws the part you're looking at.
The everyday editing is all there: tabs that come back with your unsaved changes, find and replace with regular expressions, syntax colors for 52 languages, line tools, bookmarks and printing. For data files it adds JSON and XML formatting and checking with a structure view, and "show only matching lines" turns a huge log into just its errors.
On Windows, Slate is one signed, portable Slate.exe that updates itself. On Linux it installs from a .deb with its own apt repository. ...