Talk about websites without improving their ranking
donotlink.com
donotlink.com
This is why Google created rel="nofollow"[1] and if you are really worried about where you pass PageRank to it is a much better alternative than linking to some random 3rd party site while passing value back to them.
This happened after Google discovered that people were abusing no-follow - by trying to hoard the website's weight and not sharing it with anybody.
Practical problem is, service does not make distinction between http and https schemes - typing in https://example.org/ yields http://www.donotlink.com/ZG which leads to http://example.org/.
Why not using the nofollow attribute[1]? It exists for this specific use-case.
nofollow is usually under the control of the webmaster. Which may or may not be the same as the content creator.
Think forums and blog comments, as poster you generally have no control if nofollow is added to links. Usually it should be, but no garentee.
Also think of sites like twitter, facebook and g+, again you can't ensure that nofollow is added. Similally when that content is then copied or syndicated. You can usually hope that the copier will perserve the link itself, but they may or may not choose to 'nofollow' the copied link.
And lastly, 'bad' bots, may well ignore the nofollow anyway. It would have to be broken/clever bot to get the destiniation from donotlink
edit: or if they get hacked and the same happens
Always use nofollow.