Sim-on-a-Stick. If you want to try OpenSim, this is probably the easiest way with ready-to-use installations for a USB stick.
opensim
Lumiya Viewer - About Lumiya. Very nice - a graphical SL and OpenSim client for Android. I must definitely try this out in a few days. For iOS, I still only know Pocket MV, but it can only do maps, chat, and stuff like that, no graphical rendering of the environment.
Metaverse Ink Blog» Blog Archive » The 4,096 “bug”. Why OpenSim operators should set up their grids with region coordinates below (4096,4096) - the higher coordinates simply cause too many problems and it doesn't look like these problems can be easily and compatibly fixed. Since region coordinates are internal to the grid, it shouldn't be a problem if multiple grids lie in the same coordinate ranges.
PayPal Money Module « Snoopy Pfeffer’s Blog. The original article in which Snoopy describes a bit more about the extensions to Adam Frisby's DTL PayPal Money Module. Not up to date regarding installation, but the features still fit.
SnoopyPfeffer/Mod-PayPal - GitHub. I should take a closer look at this, as it allows you to use PayPal as a money module in OpenSim. It might be interesting if I ever want to revive and share my OpenSim projects again. It is based on OpenSim 0.7.1, so I can only try it out when the new Diva D2 is released (which is already in the works).
Technology - Canvas Viewer - interesting project, uses Unity3D as a platform for a Second Life and OpenSim client. If this works and is freely available for OpenSim Grids, that would be a nice window from the web for my MiniGrid..
offline_messages for OpenSim here in a PHP version. I should take a look at it, actually I should be able to build something in Python from it that I can then use.
OpenSimulator GForge - since I'm playing around with OpenSim again, here you can find a lot of projects around OpenSim.