Here is a list of the features:
-PNG viewing (pictures (only 480×272))
-EBOOT Loading from within PSP-OSS
-UMD Loading from within PSP-OSS
-Fully skinnable (reboots the OSS to change skins)
-Wallpapers changable while in the OSS
-NEW: File Browser
-Many more features…
At the moment, PSP-OSS should only work for firmware 1.5.
They doubt >= 2.0 support will be in their first BETA. Maybe not even until kernal mode is ready in 2.0 and higher.
Early version available for the public hopefully available by Christmas.
You can download a video of it in use here.
This is something I am eagerly anticipating as it looks great. Right now I use PSPWindows which is ok, but not nearly what I am looking for. I will be downloading this as soon as it is released and will talk about my experiences in forums when I do.