Chris Johnstone's "Binary Keyboard" is an open source hardware, Arduino-based two-button input device that you can build for yourself, if you have the urge to key data directly to your computer in binary (don't worry, you can configure it to be little-endian or big-endian for ease of use).
Each byte can either be typed from most significant bit to least significant bit (left to right), or least significant bit to most significant bit (right to left). This is set before uploading to the board. After all 8 bits have been entered, it will type out the ASCII value equivalent of that binary valiue. The Pro Micro has native USB support, which means it acts just like any other keyboard.
If both keys are held down, the keyboard will switch to "1/0 mode" / "single button press mode" (I'm bad at names). In this mode, each key will represent a '1' or a '0' just like on a traditional keyboard, no binary involved.
BinaryKeyboard [Chris Johnston/Github]