They are tools that automate the link building process. xRummer is a little bit expensive (~ $550) but you can try Scrapebox which is really popular nowadays and quite affordable too. I don't really like SeNuke, I prefer to use my own custom made bots to automate the social bookmarking submission process. According to rumors the new version of SeNuke is going to be a killer. I have no idea when it's going to be released though.
They are things to keep away from unless you are very careful and know what you are doing, or want to get banned in serps
Why to keep away from them when they are just building links for you automatically ? And yes I also like xRumer
Btw: How good is Backlink Engergizer ( Wordpress Plugin ) . http://backlink-energizer.com This is their site. How good it should be ?
xrummer is a forum spammer and if you own a forum you know how much of a pain this thing is. scrapebox is very slick but is used like xrummer but for blogs. The cool thing is it scrapes through search engines for any keyword you enter and finds blog pages where you can comment and shows the pr for that page. So it literally finds you high pr blog posts where you can leave your comment with a link back to your page. It does some other very cool things that I use but I can't give away those secrets. I have not heard anyone else doing what I do with it. senuke is another tool mainly used by spammers to auto create accounts for article directories, 2.0 sites etc. Then you can auto post spun content to these sites. It is ok to help automate some stuff but many of the sites it submits to will not accept your content. So the success rate is low. All of the top sites like hubpages, squiddo, ezine articles are better to hand submit to. All of these tools can be used in a whit hat way. If you get greedy and try to create massive backlinks then you will just get kicked out of Google. You need to master these things and know what you are doing. I like to use these programs to help automate a few things and to help dig up some good sites for backlinks.
Forgot to mention senuke does the whole bookmarking thing too. So many people don't use senuke correctly. They just fire it up and start submitting. All you will do is create a bunch of 0 pr backlinks. If you can use it as a TOOL and use parts of it then you can build up some very high pr backlinks.
I understand scrapebox can make thousands of backlinks for a site. Is there a formula you should use to see how many links you should try to add on a monthly basis?
Scrapebox is a great tool that constantly updates and has the ability to download user made add-on's to further tweak the tool for your own preferences. To some extend you can even post on forums but I am not 100% sure it can totally automate the process.