Unicorn is a Unix and LAN/localhost-optimized fork of the Mongrel HTTP server. It takes full advantage of functionality exclusive to Unix-like operating systems. It will reap and restart workers that die from broken apps, and there is no need to manage multiple processes yourself. Load balancing is done entirely by the operating system kernel. Requests never pile up behind a busy worker. The server does not care if your application is thread-safe or not, as workers all run within their own isolated address space and only serve one client at a time. All Rack applications are supported along with pre-Rack versions of Ruby on Rails via a Rack wrapper. It also supports atomic log cycling, nginx-style binary re-execution without losing connections, before_fork and after_fork hooks, and optional copy-on-write-friendly memory management.
LiteSpeed Web Server is a high-performance, secure, easy-to-use, and Apache interchangeable Web server. It supports HTTP/1.1, SSL, CGI, FastCGI, LSAPI, PHP, JSP, Servlets, GZIP compression, chroot, IP level throttling, connection accounting, DoS attack prevention, and instant recovery mechanisms. With its Apache compatible rewrite engine, .htaccess, and MS FrontPage support, migration is quick and easy. A Web interface is included for administration and configuration. It can be used as a content accelerator, compression proxy, or a security guard running in front of any Web and application server.
Rainbows! is an HTTP server for sleepy Rack applications. It is based on Unicorn, but designed to handle applications that expect long request/response times and/or slow clients. For Rack applications not heavily bound by slow external network dependencies, consider Unicorn instead as it simpler and easier to debug.
BitNami RubyStack provides a fast, easy way to develop and deploy Ruby on Rails applications. It includes Ruby, Subversion, MySQL, SQLite, ImageMagick, and several Ruby Gems, and will optionally install Apache 2.2 with rewrite and proxy support. It supports Windows, Linux, and OS X, so you can share the same Rails environment on multiple platforms.
Remo is a graphical rule editor for ModSecurity, an Apache security module. ModSecurity is quite difficult to configure successfully. Modsecurity.org advertises a tested core ruleset granting you protection from most known attacks, but this is only blocks traffic known to be dangerous, when it is more effective to block everything not known to be safe. Remo is meant to assist in the difficult task of writing the rules that would correctly describe the requests that are valid for an application.
Zbatery is an HTTP server for Rack applications on systems that either do not support fork(), or have no memory (nor need) to run the master/worker model. It is based on Rainbows! (which is based on Unicorn (which is based on Mongrel)) and inherits parts of each. Zbatery supports your choice of all the thread/fiber/event/actor-based concurrency models and Rack middleware that Rainbows! supports (or will ever support) in a single process. Zbatery will still exploit certain features of Unix for transparent upgrades, log reopening, and graceful stops, but does not rely on them for basic functionality.