I need a reverse auctions tool or a free platform to manage auctions.Anyone can help?

You can try radscripts.com (I am not affiliated with them) or you can have a custom script made out for you.

Do not ever buy radlance, radbids, radclassified, radnics, radlinks or any of the scripts sold by radscripts.com

Buying Radlance Gold was my biggest mistake in 2006. I paid $300 but I don't get the script. What I got was the privilege of getting the boss to install the script at his pleasure. When I moved to a new server a few months later and asked him to reinstall the script on my new server, <name snipped> ignored me completely (the boss of radscripts). I could not do it myself because he alone holds the install code and some vital code is encrypted. So my website was
dead before it even started & $300+ gone. I have the paypal receipt as proof. This guy is friendly with you until you part with your money.

I am still blaming myself for my own stupidity for not doing enough research on this guy before my purchase. Because of bad reviews, he had removed all his listings in hotscripts.com.

Do a search on the number of websites he hung out to dry after getting their money.

The scripts they sell also have a lot of security bugs.

I managed to save someone else's review on hotscripts before Ed Pakstas removed his listings:

Great script, but..., Jun 29, 2006 Reviewed By: bolooroo
Review Of: Auction Software - Freelance in PHP :: Auctions

Radscript is great script and included lots of features that any other scripts can't beat. However, <name snipped>, the author, doesn't help you much with the customization. You're only limited with his options and he'll forbid you to go through his "precious" script. If you annoy him with bunch of emails, then he will ban your email address. So you're pretty much on your own. There is no forum support, only emails. Even emails, don't expect so much from him. His answers won't resolve your problems. PERIOD!