Closest thing to that is DSLinux. However, it sounds like you want something that will let you launch multiple *.nds files at the same time, which simply isn't possible due to the way that the DS hardware works and how programs run.
For Facebook I know m.facebook.com loads very nicely on a PSP. I invite you to give that a shot on a DS as well. I would now and tell you my results but my router is down. (Neighbors internet ftw) I will register a twitter account when my router is back up to give this a shot!