They sent four vouchers worth $25 apiece to all registered voters, who could give them to “participating candidates in municipal elections who agree to observe individual contribution limits.”
The results from the 2017 election cycle were that "Democracy vouchers doubled the number of people making donations compared to cash donors in that election cycle, and voucher users were more representative of the city’s population in terms of age, race, and income"
Sounds like an innovative approach to increasing voter engagement/participation at the local level and ensure that donors are representative of the city's population.