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Education & science
Handdrawn
Brainy Icons Free — 36 Science and Education Icons
Talking, Comments, hand-drawn
Black
64x64
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Mixed
Smooth
Tango Icon Library
Dialog, Information
512x512
warning, Dialog
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UI
Pixel
Lynx Black
ok, Dialog
24x24
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Computer & hardware
Crystal Project
stock, Dialog, warning
32x32
3D
Gnome Web Icons
yes, ok, tick
bulb, Idea, light
password, Gnome, 64
Dialog, Faq, help
Business & finance
Glyph
Wireframe mono icons
live chat, speech, talk
48x48
Web Design Creatives
Dialog
128x128
Ultimate Gnome
256x256
Dialog, Error
Discovery
Dialog, warning
Desktop apps
Free Applications Icons
red, tick, yes
Human o2
Dialog, tux, question
Gnome icons
Form, Dialog, Letter
Dialog, Form, show
Tango
Dialog, Idea, Information