Question: I have a system which has the following structure:

Inbound > Open > Pending > Awaiting reply > Ready > Closed

I'd like to use single-words, so the one that sticks out like a sore thumb is "Awaiting reply".

I obviously can't use "Pending" because that's already in use. And "Awaiting" is too similar to "Pending".

Is there a word for "waiting for a reply"?

Answer: 
How about "Unanswered"?

I know it's not the perfect answer -- it's not clear whether the items are unanswered by other people or unanswered by you. But then, the same could be said of "awaiting reply" :-)
How about "receiving"?
It suggests the expectation is still in the air. The act of receiving is not completed, hence: awaiting continues. 
Furthermore, "receiving" implies the "reply" part rather neatly. What can you "receive" if not a delivery of something (like mail, food, kisses, or just a... reply)?