With this plugin you can easily create polls in Craft plugin, without the need of an external service.
Optionally, but you will use this often, a pre-configured field type 'selectPoll' is created.
You can add this field to your existing content entries to attach an existing poll to your entry, or even create a new poll directly from within your article entry.
If you want to have anonymous users to participate in your poll, it is always unsure if a user already has participated.
The plugin keeps the latest poll submissions in a cookie, so someone using the same browser and computer will not be able to participate twice.
This might be sufficient for some purposes and simple sites. However a user might always open an incognito browser or clear his cookies; he or she will then be able to participate again.