Ultimate Member is described as 'powerful and flexible plugin that makes it a breeze for users to sign-up and become members. The plugin allows you to add beautiful user profiles to your site and is perfect for creating advanced online communities'. There are more than 10 alternatives to Ultimate Member for Self-Hosted solutions, Wordpress, Online / Web-based and PHP. The best alternative is BuddyPress, which is both free and Open Source. Other great apps like Ultimate Member are Paid Memberships Pro (Freemium, Open Source), User Meta (Freemium), WP-Members (Free, Open Source) and WP User Frontend (Freemium, Open Source).
The s2Member® Framework (free) integrates with PayPal Website Payments Standard (also free). Sell "Buy Now" or Membership access to your site. Restrict access to Roles, Capabilities, Posts, Pages, or anything else in WordPress.