What are you talking about? You can use the software however you wish. Even "in a proprietary environment" (like you can run LibreOffice in Windows).

What you mean is probably copyleft licensing which is only a subset of free software licenses. Copyleft means that you cannot redistribute the software and its derivatives unless you give the freedoms down the road to your clients/users as well.

However, there are free software licenses that aren't copyleft too.