What's the difference between pledging and donating?

Pledges are direct investments in the game's development;  They are completely non-binding, and can be decreased or retracted at any time.  Nor do they require any personal or payment information (except a contact email address).  Pledges will only be collected once the total of all pledges is greater than or equal to the projected game budget.  When collected, they will become part of a fund specifically earmarked for the game's development.
 
Donations, on the other hand, are voluntary, non-refundable contributions to the project's general fund;  They will most likely be used to meet ongoing costs such as website hosting and project promotion.
 
Both kinds of support are greatly appreciated, and will count towards determining membership status (see the "Membership" section for more details).