Employee options are the most similar to forward start options. Forward start options are a type of exotic option that starts at a future date, known as T1, and expires at another future date, T2. This feature allows investors to benefit from future price movements. Employee options share a similar characteristic. In the case of employee options, the employer pledges to grant an at-the-money option at a future date. This means that the strike price of the option is the same as the market price of the underlying asset at the time of the grant. This similarity in structure and functionality makes employee options the most analogous to forward start options.

Choice A is incorrect. Warrants are a type of derivative that confers the right, but not the obligation, to buy or sell a security – most commonly an equity – at a certain price before expiration. The price at which the underlying security can be bought or sold is referred to as the exercise price or strike price. While they do offer flexibility in terms of timing, they do not have the specific feature of setting a future start date for the option like forward start options.

Choice B is incorrect. Butterfly spread options involve positions in options with three different strike prices and are typically used when anticipating minimal movement in the price of the underlying asset. They do not bear resemblance to forward start options as they don't allow for altering expiration dates and strike prices at future dates.

Choice C is incorrect. Gap options are contracts where payout depends on whether the underlying asset's price changes beyond a certain level (gap level). They differ from forward start options because their payoff structure depends on whether this gap level has been reached rather than having an option that commences at a future date.