OS on Arduino's

[system]

Hello, I've recently been very interested in the RTOS that have been coming out for Arduinos. I've done some light research but I can't seem to find the answer to my question. Does anyone have any experience with using any RTOS with an Arduino Mini 04/05? I'm working on a project that requires the use of a Mini 04/05 and I'd like to try to use an RTOS on it. I did a bit of research and noticed that the chips used on the Uno and the mini are the same ATmega328. And some RTOS work on the Uno but I'm wondering if anyone has tried it or any confirmation on this before I purchase the necessary Arduinos. Or my other option is to find a way to use whatever microcontroller chip that can do all of that and take it off the Arduino unit and straight onto the PCB but that's my last alternative to look into.

Edit: Also sorry if I'm in the wrong section, figured since this was a project this might be the right one but I also noticed the Microcontrollers section.

[CrossRoads]

You can use the IDE to load your sketch, RTOS or other, into a '328P mounted on a standalone board.
Here's a couple of examples - if you look (and not all that hard) you can spot the '328P, xtal, caps, and reset pullup resistor that is basically the "arduino" hardware.
USB/Serial adapter can be onboard or off board, same with the voltage regulator, can be onboard or an offboard source (wallwart).
As for RTOS, several have been discussed in the forum, shouldn't be hard to find a topic about them.