Image Compression:

• Tinypng: To compress Image files for Web. WebP, PNG and JPEG compression.
• Squoosh: Squoosh is the ultimate image optimizer that allows you to compress and compare images with different codecs in your browser.

Blackboard/ Brainstorming tool/ Drawing Tool:

• Excalidraw: Excalidraw is a virtual collaborative whiteboard tool that lets you quickly sketch diagrams with a hand-drawn feel.

Colour:

• Htmlcolorcodes: Easily find HTML colour codes for your website using our colour picker, colour chart and HTML colour names with Hex colour codes, RGB and HSL values.

Background Image Remover:

• CutoutPro: Background removal, passport photo maker.

Photoshop Alternative on Cloud

• Photopea: advanced image editor. Free online editor supporting PSD, XCF, Sketch, XD and CDR formats.

Favicon Creator

• Favicon.io: Favicon generator

Stock Image

• Unsplash: Better than any royalty free or stock photos.
• Freepik: Free Graphic Resources.
• Pexels: Free stock photos & videos

This is not a complete list.
To Be Continue…