What are OSQA's best features?

Isn't the honest answer pretty much: It lets you build a niche-market QA site that works somewhat like Stack Overflow or Server Fault, and on an open-source foundation? The Stack Exchange system lets one launch a community QA site for a topic you have interest in, but follows a guiding principle that it's best to have only one really good site for a given topic, and so everything is centralized.

That actually works really well and Stack Exchange and the associated sites are awesome, but it'd be nice to apply a similar solution to smaller, more local problems. Like a Q&A site within one institution, for example. That's never going to have the global following to make a good Stack Exchange site, but OSQA lets you launch and run your own.

It's clear from the OSQA blog that merely being a Stack Exchange clone isn't the limit of the program (or of the ambitions for it), but clearly a huge chunk of its appeal is in being able to work in a similar way.

I noticed you asked the same question on the Shappado site. I suggest you try setting up your site with both (and Askbot as well) and see what works for you. That is what I did.

OSQA's biggest advantage over Shappado is that you can easily find hosting on which it will run (not necessarily easily though!). Shappado's biggest advantage of OSQA is that they offer a hosted version which will give you a site that is up and running in a few minutes.

Realistically, if you want self-hosted Shappado you need a VPS (or a dedicated server), so Shappado is more work if you host it your self, but its less work if you let them host it.

I have only read the basics of Shapado so I can't give an in-depth comparison. We wanted to installed a StackExchange-type Q&A system in-house. Both can do that.

Some of the obvious differences which lead me to look at OSQA were: it's in Python, using Django and MySQL, and under the GPL. Shapado is in Ruby, using Ruby-on-Rails, and mongomapper and mongodb. We have no experience with those technologies, and if you read the OSQA FAQ, it's the same reasons which lead to the development of OSQA.

I also like the look of the base OSQA installation over Shapado's, which seems rather heavy/thick-looking to me. This is just a styling issue and can be changed without much work. I just like that the default is more the way I like it.

Personally, I like that OSQA is stable and robust. We operate numerous OSQA sites, and they are rarely ever a problem as far as server stability is concerned.

The admin is pretty nice, too. It makes it easy to adjust tons of different preferences to your personal tastes.