Google C++ development conventions outlaw exceptions, RAII, RTTI and bans the default parameter in parseInt(number, radix=10).
Qt API style guide is brilliant, but only covers interfaces.
The Robert C. Martin series Clean Code has M104 galaxy on the cover, but it is 462 pages long and based on Java, with no simple "do this" digest.
Assuming that it is important to synchronize style and best practices across the organization, what is the smartest, most pleasant and useful conventions document you have worked with?