"Idealware, a 501(c)(3) nonprofit, provides thoroughly researched, impartial and accessible resources about software to help nonprofits make smart software decisions." The site offers a wide variety of free reports, articles, and links to information on Internet technology, social media, and use of software -- including for boards and other volunteers.
Free online volunteer scheduling service with a lot of useful options, especially template sign-up sheets and reminders to volunteers via e-mail and text. There are also fee-based premium levels for very large organizations.
Capterra has collected a long list of software, some of which are for volunteer management tracking, others for things like scheduling volunteers, and still others mainly for financial donor management. A good starting point to compare products.