Lain Browser is:
Written in C++
Open Source and has reviewable code
Still in development!
Lain Browser is a browser developed by 4channel's /g/, here are links to the thread that started it all:
Serial Experiments Lain was written by Yoshitoshi ABE, and released by TV Tokyo. Lain Browser has no relation nor is it endorsed by TV Tokyo, Lain Browser is not of a commercial nature, and is Open Source.
Lain Browser is under the GPLv3
This webpage is CC0/WTFPL/Unlicense