A Proxy (also referred to as a "go-between" or "mediator") is an intermediary actor (i.e. application, person, etc) in a given interaction (i.e. function, business agreement, etc) or process (i.e. workflow, legal dispute).
A Proxy Server is a server whose purpose is to route web requests on behalf of some person (i.e. using a browser in a given location blocked by a destination website or service) or an application performing request re-routing (i.e. network-layer proxy server configured to route all web traffic matching a given pattern). Proxy Servers operate at either OSI Layer-7 (Application) via a Content Filter or OSI Layer-3 (Network) via a NAT Filter.
Confusingly enough, Client Proxies are often also referred to as being "Server-side (Client) Proxies", since technically speaking they are a small piece of server-side code whose purpose is too route requests from a given client to an external destination and send the response back. However, a Client Proxy differs from Proxy Server in that a Client Proxy is typically event-driven and responds only to a specific asynchronous request, whereas a Proxy Server is a dedicated process used for filtering all network traffic on a given device, operating system, IP or group of IPs (i.e. an entire LAN of a given region's ISP).
Client Proxies are most commonly used within WebApps & RIAs to circumvent the same-origin policy of most modern browsers, Proxy Servers are most commonly used to circumvent intranet (i.e. government or corporate) firewalls or other network restrictions/limitations.
- F5 - Load Balancer: https://f5.com/products/big-ip (BigIP by F5 is the industry's leading Load Balancer)
- HAProxy: http://www.haproxy.org/ (reliable, high performance [TCP]/[HTTP] Load Balancer)
In computer networks, a reverse proxy is a type of proxy server that retrieves resources on behalf of a client from one or more servers. These resources are then returned to the client as if they originated from the Web Server itself.
- ngrok: https://ngrok.com/ | DOCS (HTTP/HTTPS/SSH/FTP/VNC/RDP tunneling through NAT & local Firewalls)
- HideMyAss: http://www.hidemyass.com
- Unblock.US: http://www.unblock.us
- FoxyProxy: http://www.getfoxyproxy.org
- Charles Proxy: https://www.charlesproxy.com/ (Request/Response Interception & Inspection, Throttling, Breakpoints, SSL Proxying, Reverse Proxy, Port Forwarding)
- Telerik - Fiddler Proxy: http://www.telerik.com/fiddler (Web Debugging, Performance Testing, HTTP/HTTPS Traffic Recording, Web Session Manipulation, Security Testing)
- Squid - Reverse Proxy Mode: https://wiki.squid-cache.org/SquidFaq/ReverseProxy
- The Server-Side Proxy: http://bcmoney-mobiletv.com/blog/2009/05/01/the-server-side-proxy/ (example of a Client Proxy)
- FoxyProxy - proxy servers: http://getfoxyproxy.org/proxylists.html 
- Introduction to modern network load balancing and proxying: https://blog.envoyproxy.io/introduction-to-modern-network-load-balancing-and-proxying-a57f6ff80236
- Setup your own Proxy Server in 5 Minutes for Free: http://www.labnol.org/internet/setup-proxy-server/12890/
- Use Hulu, Pandora, or the BBC iPlayer from any country: http://downloadsquad.switched.com/2008/09/19/use-hulu-pandora-or-the-bbc-iplayer-from-any-country/
- Building a Server-Side Proxy: http://mashupguide.net/1.0/html/ch10s04.xhtml
- Using XMLHttp to make calls with a proxy: http://support.brightcove.com/en/docs/using-xmlhttp-make-calls-proxy
- C# - Fast, Scalable, Streaming AJAX Proxy - continuously deliver data from across domains: http://www.codeproject.com/KB/ajax/ajaxproxy.aspx
- Bypassing Basic Authentication Using the BrowserMob Proxy: https://www.softensity.com/browsermob-proxy-qa/ (useful for Automated Testing such as Selenium test suites/cases)
- Connect through a Proxy in JAVA: http://www.rgagnon.com/javadetails/java-0085.html (how to get out of your corporate Firewall through a proxy, if one is available)
- How do I set the proxy to be used by the JVM: https://stackoverflow.com/questions/120797/how-do-i-set-the-proxy-to-be-used-by-the-jvm
- Pass Through a Corporate Proxy in Java: https://www.laurivan.com/pass-through-a-corporate-proxy-in-java/
- If the Charles SSL Proxy shows me sensitive data, is that data insecure/exposed?: https://security.stackexchange.com/questions/210356/if-the-charles-ssl-proxy-shows-me-sensitive-data-is-that-data-insecure-exposed
- wikipedia: Proxy server
- wikipedia: Reverse proxy
- PHP streaming proxy: http://blog.nazdrave.net/?page_id=7
- F5 FAQ - What is a Load Balancer?: https://f5.com/glossary/load-balancer
- F5 fixes high-risk NGINX Controller vulnerability in January patch rollout: https://portswigger.net/daily-swig/f5-fixes-high-risk-nginx-controller-vulnerability-in-january-patch-rollout
- How to Configure HAProxy as a Proxy and Load Balancer: http://dzone.com/articles/how-to-configure-ha-proxy-as-a-proxy-and-loadbalan
- What Is a Reverse Proxy Server?: https://www.nginx.com/resources/glossary/reverse-proxy-server/
- Reverse Proxy - What, When, How https://dzone.com/articles/reverse-proxy-what-when-how
- How to NGINX Reverse Proxy with Docker Compose: https://dzone.com/articles/how-to-nginx-reverse-proxy-with-docker-compose
- Exposing apps from an Oracle Kubernetes cluster using a Network Load Balancer for free: https://arnoldgalovics.com/oracle-kubernetes-free-network-load-balancer/
- FoxyProxy request filter patterns: http://getfoxyproxy.org/patterns.html