I know there are general licence comparison pages, but if I want to know whether a specific feature currently requires the PRO licence, how can I check it?
If I’m not mistaken, some features that used to be only in the PRO licence some time ago are already included in the personal edition (such as static batching), so where can I check if a feature needs the PRO licence right now?
When Unity 5 came out, almost every pro features was released in the free version. You just can’t have the cloud saving and a different splashscreen, and some small stuff.
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If you click on the question mark next to “Engine with all features” on the links in the other answers, you go to a page that lists all the features that Unity has: http://unity3d.com/unity/engine-features
In general, unless it’s a feature that is explicitly listed as pro only, it should be free.