Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. You install it in front of any server that speaks HTTP and configure it to cache the contents. Varnish Cache is really, really fast. It typically speeds up delivery with a factor of 300 - 1000x, depending on your architecture.
etcd is a distributed key-value store, used as shared cluster configuration backend. It automatically elects a master server, allows dynamic config data with optional TTLs, provides a JSON API over HTTP with TLS and long polling, uses the Raft protocol for distribution. It's the basis for CoreOS, integrates with fleet/systemd, and thus also provides service discovery.
Insomnia is a beautiful cross-platform application for organizing, running, and debugging HTTP requests.
The Embedthis GoAhead™ web server is one of the world’s most popular embedded web server deployed for over 15 years in hundreds of millions of devices by industry leaders and startups. It is compact and requires less than 150K RAM. GoAhead uses an event-driven, non-blocking core to efficiently operate with minimal resources. Coupled with a role-based authentication framework and security sandbox, GoAhead is highly secure. It is easily embedded and ported to create secure web applications.
Embedthis Appweb is a fast, little embedded Web server. It is unmatched in efficiency and serves pages at native speed, using an event-driven, non-blocking core to serve multiple requests using minimal resources. It has integrated caching and the ESP "C" Web framework. Without compromising performance, it has extensive security controls and a rigorous security sandbox that helps protect the server and mitigate denial-of-service attacks. It is one of the most widely deployed embedded Web servers
GNU wget is a HTTP and FTP downloading and mirroring tool for the command line. It provides various options and complete HTTP support. It supports REST and RANGE requests for partial and continuous downloads, can use wildcards for mirroring complete websites, converting HTML references to relative links, use HTTP cookies, proxies, persistent connections, background processing, and can compare files prior downloading.
Hiawatha is a free and open source webserver for Unix. This project aims at writing a webserver that is secure, easy-to-use and lightweight.
Configurable, non-interactive HTTP server that executes shell commands in response to network requests. Comprehensive filtering of the requests is possible through command-line text tags. Offers minimum dependencies and statically build executables. Linux and Windows builds available.
lighttpd is a secure, fast, compliant, and very flexible web-server that has been optimized for high-performance environments. It has a very low memory footprint compared to other webservers and takes care of cpu-load. Its advanced feature-set (FastCGI, CGI, Auth, Output-Compression, URL-Rewriting and many more) make lighttpd the perfect webserver-software for every server that suffers load problems.
Apache is the most widely used open-source HTTP server for modern Unix-like systems. It descended from the original NCSA HTTPd server, but accumulated a wide array of configuration options and features and extension modules since. It stays current with recent HTTP protocol changes and even SPDY support.
curlcpp is a C++ wrapper around cURL/libcurl. It abstracts connections and transfers in a more user-friendly and object-oriented API, through curl_easy, curl_multi and curl_share. It provides tracebacks, and a curl_writer interface for output capturing, and simplified data transfer handling via curl_reader/writer.