Very rare asset with impressive tech potential. One of the shortest domains on the internet ever.
For sale:

4.cr

You can use it for website shortening http://4.cr , for making exremly short e-mail addresses like i@4.cr , me@4.cr and many other applications.

Real Latin1-charset 1-character domains in the format L.LL are very limited since any country offers only 36 such domains. Also many countries have reserved them for future use so they are even more limited. They are also popular objects of investment.
Possible meanings for "CR" can be: CReative, CRedit, Carriage Return, Cross Reference, Czech Republic (alt.)

Sale and details: http://1-single-letter-domains.com/?rl=u10.4cr.b#1chars