I have swapped/exchanged some links with different sites in the past, but as the time goes, some of them don't exist anymore or they have removed the links to my site. Is there any good way of tracking is the links still exist? Any open source software which would keep track of the backlinks?
If by "some" links you mean a dozen or two then manually tracking them once every 2-3 months should take 5 min and work just fine. If you really have so many exchanged links that managing it manually is impossible then 1) I would reconsider your link building strategy and 2) Google can probably provide you with lots of automated back link tracking solutions.
Good question - It might be a good tool for someone to build: 1. Spider your links page. 2. Verify that all the sites you're linking to still even exist 3. Spider the ones that exist, to see if they still link to you. Let me know if you find any good tool. I might be interested in using something like that too.