Are CRM open source softwares free or not ?

I have a few questions on this topic. I am searching for a open source crm software, biggest reason is because I thought they would be free.

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But the more I dig in the more I see people talking about prices regarding these softwares. So how does it work ?

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My plan was to install Suite CRM using Cpanel in the same server we host our site ( this might change, I am still figuring out if it will affect our site speed too much or not).

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Is it just not recommended to install these programs on the host server ? Is it not safe ? What should I do ?