A collection of 70 hand-picked, web-based tools which are actually useful.
Each will generate pure CSS without the need for JS or any external libraries.

Full credit goes to the authors behind each of these apps (where possible I've linked to their GH/ socials)

Contents

• Property Generators
• Animations
• Backgrounds
• Color Tools
• Typography
• Loaders
• Layouts
• Informative

Property Generators

1. Neumorphism

Generate Soft-UI CSS styles using inset shadows, by @adamgiebl

2. Shaddows Brumm

Make and preview beautifully smooth shadows, by @brumm

3. Fancy Border Radius

Generate cool shaped objects with border-radius, by @9Elements. Similar to BlobMaker

4. Glow Generator

Generate pure CSS, cross-browser glow effects

5. Clothoid Corners

Generates clothoid rounded corners by CSS clip-path, by Takehiko Ono

6. Glassmorphism

Build semi-transparent, blurred glass-like backgrounds. Similar to ui.glass/generator

7. Clipy

Generate complex shaped objects using clip-path, by @bennettfeely

8. CSS Filters

Generate and preview pure CSS Instagram-style photo filters, by @ghosh

9. Base64 Image

Encode an image directly in your CSS in Base64

10. Quantity Queries

Generate quantity-based CSS queries, by @drewminns

Animations

11. Animista

CSS animation playground and generator, by Ana T

12. Cubic-Bezier

Preview and generate advanced cubic bezier animations, by @LeaVerou

13. Keyframes

Advanced keyframe animation maker, by @mitchas

14. Wait Animate

Use animation-delay to simulate delays, by @will-stone

15. Transition.Style

Copy-paste transition animations, by @argyleink

Backgrounds

16. Hero Patterns

Find and customize simple pure-CSS patterned backgrounds, by @steveschoger

17. Haikei

Generate unique organic SVG banners and backgrounds (similar to Shape Divider)

18. Pattern Generator

Advanced pattern generator

19. CSS Pattern

Collection of pre-made pure CSS patterned backgrounds, by @Afif13

20. Patternizer

Build striped backgrounds, by @matthewlein

21. Patternify

Build your own old-school pattern, by @SachaGreif

22. Animated BG

Generate blurred animated pure CSS backgrounds, by @Vincenius

23. Trianglify

Geometric background designer (note: only semmi-free), by @qrohlf

24. Animated Backgrounds

Collection of pure CSS background animations

25. Magic Pattern CSS Backgrounds

Collection of reusable SVG-based / pure CSS background patterns, with a visual explorer

Colors

26. CSS Gradient

Advanced CSS gradient builder

27. Parametric Mixer

Equaliser-based CSS color composer. by @dawidwoldu

28. Palettte.

Develop and tweak color schemes

29. Paletton

Palette builder using opposing or attracting colors

30. Grabient

Sample gradients.
Similar to CoolHue, WebGradients.com, GradientHunt, GradientButtons and UI gradients

31. Color Hunt

Yet another color palette designer

32. Easing Gradients

Cubic-bezier style pure CSS gradients, by @larsenwork

33. Flat UI Colors

Flat-style handpicked color palettes, by @ahmetsulek

34. Color Tools

Mix, extract, convert and generate colors

35. ColorPalettes.Earth

Natural color pallets from nature

Typography

36. Font Joy

Discover and preview various font pairings, by @Jack000

37. Type set With Me

Typography & legibility sandbox, by @tsmith512

38. Type Scale

Generate heading/ body font sizes, by @jeremychurch

39. Glyphter

Create icon fonts from SVG graphics

40. Font-Library

Tagged library of Google Fonts, by @katydecorah

41. Glitter

Export 90s-style Glitter text

Loaders

42. Spin Kit

Selection of clean CSS loading animations

43. Whirl

100+ CSS loading animations, for copy-paste

44. Loader Generator

Pre-built and custom pure CSS loaders

45. lukehaas - CSS-Loaders

Simple pure CSS loading animations

46. CSSLoaders

Complex pure CSS loaders

47. loading.io/css

CSS implementations of common loaders

Layouts

48. CSS Grid Garden

Interactive game for learning CSS grid, by @thomaspark

49. FlexboxFroggy

Interactive game for learning flexbox, by @thomaspark

50. Flexplorer

Visual flexbox demo, by @bennettfeely

51. Flexulator

An interactive CSS Flexbox space distribution calculator, by @telagraphic

52. Grid Generator

Make grids using the CSS grid-template properties, by @sdras (similar to grid.layoutit.com)

53. Layout Generator

A modern CSS layout maker

54. Box Model Diagram

Just a visual box model demo

Informative

55. CSS Timeline

A history of CSS

56. Screen Size Map

View popular screen sizes for responsive design

57. CSS Ruler

Preview various CSS units relative to each other

58. bada55

List of very funny CSS hex color codes
See also, colors.lol for some overly-descriptive color pallets

59. Who can use?

Checks accessibility grade of a given color combinations, similar to Colorable

60. Can I use?

Browser compatibility check of various, CSS, JS, HTML and web features

61. Can I email?

Similar to Can I use?, but checks if a given CSS property (or HTML elem) is compatible with email clients

62. CSS Processing Tools

Convert to and from any other CSS language

63. Unused CSS

Searches your site for unused CSS, and displays stats

64. Component.Gallery

Global component search

65. Design System Gallery

A collection of open design systems, for inspiration

66. Checklist.design

A collection of design best practices organised as checklists

67. Glyphs

A list of CSS glyph character codes (see also GlyphSearch for library icons)

68. CSS-Tricks.com

The best CSS blog out there

69. Curated Design Tools

A curated list of awesome design tools

70. Awesome-CSS-Frameworks

A list of open source CSS frameworks

71. CSS Reference

A visual guide to CSS properties (similar to htmlreference.io)

72. MDN CSS Docs

Excellent documentation of all available CSS properties

If you like this kind of stuff, consider following for more :)