Stock option grant with an early exercise feature that lets you purchase the shares immediately at grant or at the time of the offer. However, the stock purchased is subject to vesting requirements, and thus you are essentially purchasing restricted stock. Under the RSP, the offer price must be the fair market value at grant to avoid problems with Section 409A. Usually, restricted stock purchase plans occur only at private companies. For details, see this website's section Pre-IPO: Early Exercise Options.