There are a host of alternative wood stains you can use with varying success including black coffee / tea, crushed berries and nut shells. Vinegar and steel wool is a great mix that adds great age to new wood in an ebonising effect.
Put on some protective gloves and take a roll of 0000# extra fine steel wire wool under a hot tap to wash off any rust-inhibiting oils. Make sure it is actually wire wool in the packet as I am aware there are some imitations that will not work. Pull the steel wool apart into a thin layer and place in a glass jar. Pour over ordinary white vinegar until the wool is covered. Cider vinegar is also an option. If you have some rusty nails, throw those in too and leave the jar with a loose lid for 24-48 hours until the bubbles have stopped and the vinegar is darker. Give the jar a shake every while / when you walk past it.
Strain the mix through a coffee filter or cloth to remove the small metal particles. Brush the mix on with a brush to leave a wet layer, a rag will not get the surface wet enough. Again, go with the grain when applying. Let the wood dry for a few hours and it will go a magnificent dark colour. Softwoods go a blue-grey, great for aging new wood. Hardwoods go darker depending on the tannin content of the wood. Mahogany and oak go very dark from this reaction.
This forum post documents different wood reactions to the vinegar mix.
The sharp smell will dissipate after a few days. The surface will also need a top coat of oil or varnish to protect it.