
As software developers, we often have to do some other programming related tasks while we are doing coding such as preparing an architectural diagram, explaining an algorithmic approach to a person etc. Then we feel the need for tools to do those activities. Thereafter, either we have to use a standalone software or we have to go with a quick online tool. Undoubtedly, going with an online tool will save our time and most of the time it will give great features rather than standalone software such as live collaboration.
Here is a list of great online developer tools that I found from the internet.
Diagrams.net — Any kind of diagrams and charts
This is formerly known as draw.io and now it was renamed to diagrams.net. This web application offers nice features to create any kind of diagrams you need. I often use this tool to create flow charts and architectural diagrams. Importantly, it gives us many shapes including standard icons of cloud providers like AWS (Amazon Web Services) and Azure by giving us the ability to create professional architectural diagrams for software.

Link to the web application: app.diagrams.net
AWW App — Virtual whiteboard for quick sketches
Need to explain about an algorithm during a call? Well. AWW App will help you. In addition, this is really helpful when you need to think about an approach for problem solving without a physical whiteboard or pen and paper. The most important feature is that it allows you to access previously added elements (But you can lock elements too).
This web application is also touch-friendly. Therefore, this virtual whiteboard will work nicely with mobile phones and tablet computers.

Link to the web application: awwapp.com
Debuggex — Regex visualizer tool
If you can write an error free regex with the first attempt, you are a hero. However, sometimes we work with complex regex. Then we have to make sure the regex we wrote is almost correct. Of course, regex codes with less conditional branches and groups can be visualized with our minds and also can be easily verified with several test cases. But, regex codes with many conditional branches and groups require more effort to verify.
Debuggex web application visualizes regex codes in a very friendly manner for verification/debugging.

Link to the web application: debuggex.com
IDE One — Try out any programming language online
Perhaps, we need to see how an imaginary code snippet works in reality or we need to try an unfamiliar programming language without actually installing its developer tools to the computer. IDE one is a great tool for these kinds of things. Indeed, It basically gives us the ability to try out any programming language online. Moreover, this web application can be used to pre-implement an algorithm before actually implementing the optimal one in the actual codebase.
Few years back, I used the same tool for practicing interview questions and coding challenges. This app is so minimalist because it gives us only mandatory features like code editor, standard input and output.

Link to the web application: ideone.com
Carbon — Create beautiful screenshots of code
When we are preparing a technical presentation or an article we may need to add snapshots of sources codes. It can be easily done by taking a screenshot but there is another way to do the same in an attractive way. Carbon online tool accepts a textual input and will generate a nice graphical view of source code.

Link to the web application: carbon.now.sh
Bonus — Browserling online tools store and Peek
Browserling has hundreds of small but golden online tools, especially for web developers.
https://www.browserling.com/tools
Also, I used the awesome Peek tool on Linux to record these animated GIFs. Probably, you will use it with your next article.
Did you find your favorite online developer tools within this list?