Hello guys,
MT OS has JRE or JDK itself?
I want to have apache tomcat on it, and it needs to have JRE.
If not,
is it ok to darg and drop the JRE file on File in winbox? or it should be installed on it?
thanks indeed.

ROS doesn't allow installation of packages which aren't from Mikrotik.
Then, you can't install any java.

"Also on METAROUTER you can use openwrt image to host tiny linux and its few apps in it. like APACHE, asterisk etc. web server was in highly demand by local cable operator who wanted to host NON payment/reminder page to be shown at there clients."

I mean that.

https://aacable.wordpress.com/tag/mikrotik-apache/
https://mum.mikrotik.com//presentations/CN12/jesse.pdf

by the way , I 'll appreciate if anyone shares her/his experience.

Yeah, you can run some applications on the openWRT. But only if you compile the source to architecture mips or ppc.
You can do an reverse proxy with Nginx or Apache to some Java backend in another server.

MetaROUTER is virtualization, you run another whole system inside RouterOS. So regarding required effort, it's like if you had another machine, you don't save any. And it's more limited. If you have standard x86/ARM/... machine, you can choose from several different systems. With MetaROUTER you have only OpenWRT (or some DIY solution, but you probably don't want to do that). Also in the past, MetaROUTER used to be horribly unstable, but hopefully it's just thing of past now (but I didn't check lately).