One of the key modalities in organizing a campaign is talking to other people. Canvassing apps help organize and optimize that work.

Suggested reading:

• "The effect of door-to-door canvassing is one of the largest and most robust in the get-out-the-vote (GOTV) literature and almost rivals the effect from social pressure mailings." - Bhatti, Dahlgaard, Hansen, and Hansen (2016) citing Green, McGrath, and Aronow (2012).
• A new model known as ‘deep canvassing’ is being tested in the swing areas of Pennsylvania. Micah Sifry provides an inside look in The American Prospect (2020).
• Organizing for Action (the surviving part of Barack Obama’s presidential campaign following his election) has shared their canvassing guide (PDF), which includes information about why campaigns canvass, tools, persuasion scripts, and more. By Kunoor Ojha, Aram Fischer, Tom Liacas. (circa 2009)