Spond is all about getting definitive and straightforward answers, which is the reason that 'Maybe' is not an option.
The Spond team thought long and hard about this and, while it may be fine to say you might attend a party or night out, this is not something that coaches can work with.
This is mainly because it is easier for the organiser to plan an event when they know how many will actually show up. Difficulties may arise if 10 people have replied 'Maybe' to an event, but then everyone shows up on the day. Those who are invited need to consider the event immediately, or wait to respond until they know if they can make it or not. When someone takes a long time to respond to an event, the app will prompt you to send out a friendly reminder to the people who have yet not replied.
Users that were previously surprised that 'Maybe' did not exist as an option when they started to use Spond, have later reported that it made the job of managing events significantly easier.