Nothing

we are in control of many of our choices

we are free to think and decide

we can claim responsibility for our actions

Freewill is the ability to choose and act according to the dictates of our own will

Our mind - the totality of our mental processes - does the choosing

We choose to think or not, what to think about, how much and how long to concentrate on an issue, how many options to consider, which of the options to select, etc. We also make higher level choices of goals and values, such as desirable character traits, careers, friends and lovers, and of course, moral decisions such as when to lie or tell the truth. Freewill comprises conscious choices only.

Our choices cannot and obviously should not be totally free from (or fail to take into account) our knowledge, values, and perceptions of our environment and ourselves. Our choices are not free from past thoughts and decisions, nor from external influences. Our choices can also not transcend the laws of nature, ie. do the impossible. Once we relate our mind's abilities to that of non-volitional entities, we find that the freedom in freewill is not the elimination of influencing factors as such,