- Math-Life balance, a videochannel run by Mura Yakerson.
www.youtube.com/channel/ UCYRR0SgbYH59htIHkwTbqMw - MathOverflow, a stackexchange page for professional mathematics
mathoverflow.net/ - Original soundtrack of David Hilbert speaking about "Naturerkennen und Logik" (in german)
- With this shocking application of the fundamental group it is demonstrated that clipping two carabinders together can have an unexpected effect.
www.scilogs.com/hlf/ amazing-rope-trick/ - Here one can play games like chess or tic-tac-toe on closed surfaces like the Klein bottle.
www.geometrygames.org/TorusGames/ index.html.de - It is shown how to slice a bagel into two linked halves.
www.georgehart.com/bagel/ bagel.html