Linksys for a quite a while has sold routers whose software was based on a open version of linux. Because of this they had to release the source code to the public. This got a lot of interest and many features that used to only be on high end commercial router/access points were developed by the users.
Many of the features in these hack releases have now become standard so there is not as much need. When cisco got linksys they decided to not use this linux based OS. Didn't take them long to find out that part of the reason people were willing to pay a little more for linksys was this feature. So now they release 2 versions of many of their routers.
Have not seen this particular model it is pretty new.
Go to the dd-wrt and tomato sites and read about this software. This is mostly for a more hardcore person who wants to do more than just make a connection to his network.
customizable? I am specifically talking about the Linksys E2100L. I am looking for a wi fi system and wonder if this is good. I do have a desktop computer running on Linux and will have a Mac notebook. Will this work? Is there a better one? I am new to wi fi so any suggestions are helpful.