Gleam: Easy setup, various competition mechanics, instant rewards, built-in sharing, responsive widgets, fraud protection, multilingual support.

Vyper: User-friendly, landing page builder, entry and referral tracking, embeddable, referral tracking logic, customizable templates.

Viral Loops: Viral competitions, pre-launch landing pages, email collection, referral programs, templates, waitlist campaign platform.

Campaignware: Engaging content creation, lead generation, mobile responsiveness, email automation, Zapier integration.

Woorise: All-in-one platform, conversion-optimized landing pages, contests, quizzes, giveaways, templates, built-in referrals, payment collection.

Upviral: Viral and referral campaign creation, easy setup, leaderboards, marketing automation (email/SMS), retargeting, social sharing.

Viral Sweep: Sweepstakes, waitlists, easy creation, example layouts, integrations (CRM, analytics).

King Sumo (Beta): Fast campaign building, WordPress integration, conversion-optimized design principles, created by MIT engineers.

Wishpond: All-in-one platform, funnels, landing pages, pop-ups, forms, automation, templates, widgets, landing page design options.

Rafflepress (WordPress): Email capture, referral entries, social sharing, drag-and-drop editor, tracking, retargeting, integrations.