Is Zig Zag app free?

Excuse me, could you please clarify whether the Zig Zag app is available for free? I've heard some buzz about it but I'm unsure if there's a cost associated with downloading or using it. Are there any hidden fees or in-app purchases that I should be aware of? I'm keen to try it out but want to make sure I'm not going to be charged anything unexpected. Thanks in advance for your help!