NEW YORK—As Sens. Kamala Harris, Kirsten Gillibrand and Cory Booker kicked off their Democratic presidential campaigns, they asked supporters to register for rallies and town halls, routing them all to the same online platform, MobilizeAmerica.

The two-year-old tech company, based in New York, gives Democratic campaigns and progressive causes a centralized sign-up system for events, door-knocking and shifts calling and texting voters. The volunteers’ information is saved on the MobilizeAmerica website, and they are exposed to other Democratic work if they click through events listings.

Each election cycle is an incubator for campaign tools to sell in the multibillion-dollar political market, and the two major parties race each other to come up with the best new systems. By 2016, Republicans had deployed a broadly used data-swapping system that Democrats are now trying to emulate. And in 2004, Democrats developed ActBlue, an online fundraising system that Republicans want to copy.

The co-founders of MobilizeAmerica are veterans of Democratic presidential campaigns who spotted a business opportunity in the world of political volunteerism. Large-scale campaigns amass long lists of potential helpers, but there wasn’t an easy way for busy campaigns to keep track of them, or a way to connect those people to other political events or campaigns that might be of interest.

The genesis of MobilizeAmerica came shortly after the November 2016 election of President Trump, when millions of people attended women’s marches timed to his inauguration.