Why?

Each is probably equally important:

Alignment. To better align personal incentives with the mission of the company.
Motivation. The team is what got us here. Improve the feeling of fair value distribution. e.g. If my work leads to x10 the revenues of the company. Why is my financial compensation not proportionally correlated to this outcome?
Hiring. To attract the best talent. e.g. Why should I accept the offer of MUI over Google?
Retention. To incentivize people to push the mission further for longer (stay longer at MUI, not too much, e.g. 10 years, but enough to differentiate from the competition) e.g. I have the opportunity to work on a new shiny project with a lot of potential, so why not jump ship?

Characteristics

1-year cliff, simplify the operations in case of mis-hires.
4-year vesting
Monthly vesting, not annual to avoid anniversary effects.
A light backload vesting, to match with the long product cycles in our open-source market. (TODO refine exactly)
The stock will be granted to everybody until we reach 50 people. (TODO above 50 people, we need to determine if we keep an all-employee get stocks options or only tech roles policy.)
Reserved for full-time employees, as we are in a winner takes it all market.

How many Stock options are granted?

Principle

The idea of the number of shares distributed is that if during your tenure (from when you join to when you leave) the company grows by a factor Z, then you earn in the order of Z your annual salary, e.g. Z = 10.

Definitions

gross equity value, in dollars, that they will receive (based on our compensation bands).
common stock fair market value (“common FMV”), which becomes the “strike price” or “exercise price” that they have to pay to exercise their options.