Questions about free plan

can I delete the product how many times I want

On paying plans (Solo, Basic, Plus, Premium, or Max) you can delete product keys. We don't allow it on the free plans because we were getting a lot of people cheating our system (they don't seem to see the irony).

can I revoke licenses and reuse the activations

You have a choice: you can revoke or you can delete a product key. Revoking product keys keeps a record of the activations and gives the end-user a human readable error message.

For instance, let's say a legitimate user purchases your software. You send them a product key and they're happily using your software. Then, one day someone hacks into this customer's email account, they find the product key and release it on the web. You can revoke this product key and notify them that the product key has been released on the web. When you call IsGenuine or the next time they try to activate -- let's say they deactivate on one computer and activate on another (a legit use) -- they'll get an error saying the product key has been revoked.

If you just delete the product key then they'll have no clue as to what happened.

My guess is you're just testing the LimeLM right? If the product keys aren't in actual use then you can redistribute them however you'd like.

Yes I'm a student and I'm working on a free game. My class mate are helping me in testing it, so I'm trying limelm because I don't want users that are not of the project get the game at the moment. The project is opensource but not ready to be public-released.

mmm I didn' understand what the free plan allow me to do... I have 5 total activations, so let's say 5 users. Now, can I delete a product key so that one user cannot use it again and generate a new one to give to another user?

Not on the free plan. You can revoke the product key but you cannot delete it. On paying plans you can revoke a product key or delete it.