Not for Windows
but for Unix-like OS via ConnectBot.

Easy input Ctrl key.
Each key is small, but enough keys.

How to begin to use
1. install this app
2. open "Settings"
3. tap "[Personal] Language & input"
# {
4. tap "[Keyboard & input methods] Current Keyboard"
5. tap "CHOOSE KEYBOARDS" or "SELECT MORE"
# } or {
4. tap "Virtual keyboard"
5. tap "Manage keyboards"
# }
6. set on this app to enable keyboard

publish source codes at
http://code.google.com/p/ctrlkeyboard/