These sites are definitely useful to any web developer or user

I'm not numbering it and I'm not saying which best or not I just share my personal experience to you. I generally use this site to save my time and work. If you want you can use it.

pdfcandy.com

These will help you to manage any kind of file like Compress PDF, PDF To Word, Word To PDF, HTML To PDF, XML TO PDF etc. 
 
Let's see here is the all services of pdfcandy. You can save your time by using it. I have used many such sites before but the most interesting part of this is opening menu. It is too helpful.

wordtohtml.net

next is wordtohtml. It's actually converted your text document to HTML format. If you are typing anything in word box it will give you live HTML preview. 
There is two type of view visual editor and HTML editor.
 

This is the visual editor part and here you will get more kind of tools. Font size and color control, text align, bullet, insert link option I most like. 

As I said I'm not recommending you to use this site. I just share my personal experience about these sites.

tablesgenerator.com

Sometimes I use tables generator because it's very easy to use and you can generate HTML tables by using it. Also, you can include row, cell according to your need. 
 

the most interesting thing is you can use CSS also in this table generator. Here found text decoration option such as you can bold your text, Hyperlink etc.

webp-converter.com

Many are familiar with WebP format. Wikipedia: About WebP Format -  It is currently developed by Google. The format was first announced on 30 September in 2010 as a new open format for lossy compressed true-color graphics on the web, producing smaller files of comparable image quality to the older JPEG scheme. On 3 October 2011, Google added an "Extended File Format" allowing WebP support for animation, ICC profile, XMP and Exif metadata, and tiling (compositing very large images from maximum 16384×16384 tiles). The support for animation allowed for converting older animated GIF to animated WebP. 
 

Imgur.com and Imgbb.com

Both are image uploading sites. You can upload your photo here for free. If you have a limited hosting plan then you can use it because you can save your valuable storage by using this site. But I do not upload my personal photo here Only I upload which I shared the public. 
At first, you need to sign up in this site after completing sign up process you can upload and share your photo to others. 

w3schools.com

Actually I use Tryit Editor of w3schools.com. I think it's awesome, You can create an HTML file with live preview. 
w3school website is also helpful anyone can learn to use of HTML and CSS.  More HTML and CSS examples have given in w3school. I think it is the best learning center to WEB Coding. What’s not in here, I think everything is here regarding HTML and CSS or JavaScript. 
If you are the beginner you should learn w3school.