SLeek basically is a halfway point between the full SL client and Ajaxlife. Functions such as local chat, IM, and teleporting are all available, but it also gives access to an inventory, friends list, and a people search.
Screencaps after the break.
One of the largest drawbacks of SLeek is the lack of a places search and/or the ability to select a certain point in a sim without having to know the exact coordinates. Also, I did notice that the client showed a health meter in non-damage areas, but that’s minor nitpinking.
Definitely a good choice if you want to run SL along with multiple other programs and are not worried about seeing the graphical world (or sitting down), but at least give it a run through before passing judgement on it.