What's a good app that randomly chooses winners for things like giveaways on Twitch streams?

Have a couple of decent gaming headphones that I got but don't need. Still new in box and figured that I could do a giveaway for them in a stream.

I was watching a couple of streamers who seem to have a randomizer app that selects a winner so they wouldn't appear prejudice for choosing a winner themselves.

I also would only be able to do the contest in the US because of shipping costs so I was wondering if that would run afoul of any Twitch guidelines.

Thanks in advance.