Is BIM software free?

Could you please clarify whether BIM software is available for free? I understand that there are various options in the market, but I'm particularly interested in knowing if there are any free versions that offer comprehensive features. If not, what are the costs associated with acquiring licensed BIM software, and are there any trial versions or demos that can be used to evaluate the software before making a purchase? Additionally, are there any open-source alternatives that might be suitable for my needs? Thank you for your assistance in this matter.