Line snap
A tool like "object snap", but for snapping any point on a line (wall), to be more flexible in drawing.
For example, you have a room like this:
______________
| |
| |
| | <-- line A
|_____________|
and you like to do something like this:
______________
| line A --> |
| |_____________ line B
| | |
|_____________|_____________|
To draw line B, it would be useful to snap line A at the point, where line B comes up against it.