In its latest feature test, Twitter has added polls to tweets. Users are reporting they have gained access to the feature, which lets them insert polls within their posts. Other users can vote in the polls and see the results. It is only possible to have two options in a poll, at least for right now.
This feature appears to be functioning on mobile and desktop. However, polls may not work on mobile apps created by third-parties.
Not everyone has access to the polling feature. It appears to be limited to some verified users and Twitter staff.