ShortStack

ShortStack builds the contest itself, not only the widget: a landing page, the entry form, the rules that decide what counts as an entry, and the random draw at the end. Emails to entrants go out from the same place. Pricing is by page views rather than by entries, and overage is charged per thousand once a campaign catches on.

A free forever plan runs a campaign with view limits. Paid tiers are $24, $49, $99 and $166 a month billed annually at $290, $590, $1,190 and $1,990, separated by included views, entries and features. Overage is charged per 10,000 views and per 1,000 entries at rates that fall as the plan rises. An entry API and CSV export sit on the paid plans. Nonprofits are offered 50 percent off every tier.

Marketers and creators running contests where the rules matter and the entries need to be defensible. Somebody wanting a simple viral-loop widget on an existing page should look at Gleam or KingSumo.