The folks over at Opensim have been developing their code for more than two years now (it will be in its third year in January 2010), and it is still very much in the alpha software phase.

One of the reasons for this lengthy alpha phase is due in no small part to all the extra work in creating cross-platform code (Opensim is available in Windows and Linux versions, and can be run on Macs using the Mono package for OS X)

Unfortunately, further delays are likely due to ongoing problems with Mono. One of the core developers at Opensim, Melanie, made this post in the Opensim Developers Mailing List:

after discovering a bug in the 2.0.1 version of mono, which causes frequent crashing of regions, we have taken the step to bump the minimum required mono version to 2.4.2+.

This has become necessary because the bug is rather difficult to isolate and therefore impossible to work around reliably.

We do understand that this may cause difficulties for some people, who have been relying on packaged binary versions of Mono. Version 2.4.2 is recent enough to have no binary packages, so it will be necessary to build Mono from source. However, we feel it is unavoidable at this time, as we can't recommend or endorse a Mono version that we know to contain a showstopper bug.

On the upside, 2.4.2 has much better performance and stability, compared to 2.0.1.

However, Nebadon Izumi, who operates the OSGrid, the largest Opensim grid, had this to say in response:

I hate to say this, but there is absolutly no safe or stable version of mono from my perspective, it doesnt matter what version of mono OSgrid is running, our plazas are crashing all day long, we are lucky to get 30 minutes in a region that has people in it.. for well over a month now our Speedbuilds and Primwords games on Sunday and our Tuesday Meetings have been absolutely terrible. I honestly dont think it matters what version of mono your running, they are all quite terrible in terms of providing any kind of stability or performance. So i have to -1 this bump theory, I dont think its valid honestly. Can you be more specfic about the bug and why you dont think its present in later versions of mono? and maybe you can explain why our Windows based regions can run for weeks at a time, while our Mono plazas cant even seem to run a full hour?

So for now it appears that the Linux version of Opensim has gone off the MonoRails, let's hope it gets back on track before too long.

Rock

Full thread here (Mono Minimum Version Bump, 28th Sept 2009)