The key problem with developing for Second Life thus far has always been the less than sufficient APIs that Linden Lab offers.

When it comes to communicating with objects in-world, you have the choice of the reliably broken XML-RPC, polling from in-world via llHTTPRequest(), or sending bite-sized data snippets by email. To make it easier, faster, and more flexible, MetaverseData introduces the Message Exchange Service that makes this task painless.

Interacting with avatars (say, sending message, or delivering a product) can be just as much of a hassle. Everything is dependent on their UUID also known as their "key". If you don't have it, you can't do it. Again, Linden Lab currently does not offer a useful way of acquiring the UUID, making transparent web applications that much harder. MetaverseData offers Avatar Services that let you look up avatar related information easily via REST calls.

Getting a list of region data used to be fairly straight forward task; everything was embedded in the JavaScript file that was part of the MapAPI which was used by SLURL.com. With Linden Lab switching to Google Maps and custom map tiles all that went away. [I believe this is an effort to conceal the size of the grid.]

Finally, uploading textures into Second Life has only been possible using the Second Life client. The Texture Service allows you to send an image in pretty much any format, converts it to JPEG2000, uploads the image into Second Life, and returns the UUID which you can use in your Second Life scripts to interact with the image in-world.