CronLess - Make scheduled requests
PageSpeed Insights ,varvy pagespeed, pagelocity Insights about page Speed
dotnetfiddle - Test your C# code online with .NET Fiddle code editor.
Linqpad - Connect in databases, write queries in C # / sql, or test statements in C #
mockbin - Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
PostMan - Postman is postman :)
Plnkr - Plunker is an online community for creating, collaborating on and sharing your web development ideas.
Fiddler - Fiddler is a free web debugging tool which logs all HTTP(S) traffic between your computer and the Internet. Inspect traffic, set breakpoints, and fiddle with incoming or outgoing data.
ExpireBox - ExpireBox is the best free temporary file hosting service, you can share big files with family, friends or colleagues. Your file will be deleted after 2 days.
WeTransfer - WeTransfer is the simplest way to send your files around the world. Share large files up to 2GB for free.
Mailinator - public email
JsonGenerator - Generate any random data you want with power of agile templates and save it to our servers for later use.
QuickType - quicktype generates types and helper code for reading JSON in C#, Swift, JavaScript, Flow, TypeScript, Go, Rust, Objective-C, C++ and more
FlyWay - Version control for your database. Robust schema evolution across all your environments. With ease, pleasure and plain SQL.
Liquidbase - Source Control For Your Database: Liquibase is an open source, database-independent library
EditorConfig Reference - from KentBoogarart, nice post explaning standards for c# developers.
https://www.jam-software.com/treesize_free
http://docfetcher.sourceforge.net/en/index.html