[jakub_g]

You can exploit this trick to some extent to name a file in a way that spoofs its real extension. E.g. name an .exe file such that it looks like if it was .doc (and give the exe an icon associated often with .doc to be even more convincing).

[13]

Works on URLs too.

‮http://myspace.com/#/segami/moc.koobecaf//:sptth

[joelthelion]

Pretty dangerous, but at least my browser corrects it in the address bar.

[cnrsvxz]

This has been done by FinFisher:

https://www.youtube.com/watch?v=sW-N7qQU-tA#t=14m04s