How might I discharge a sump pump, furnace condensate line, and water softener to a single floor drain?
Is it possible to run the softener hose and furnace hose over to the sump pump? I am assuming you have a furnace distillate pup already.

If it is, perhaps you can discharge them there into the sump pump pipe itself, or BETTER snake another pipe down inside that pipe to the drain. 

You may have to get creative drilling a hole into the end cap so the smaller pipe is a tight fit and glue it together so it is water tight.

You do not have to go all the way with the concentric pipe though if there is a decent slope on the existing pipe, but since the outlet is so close to the top of the floor drain, I doubt there is.