What is the replacement for the RB493?
why almost all RouterBoard are Discontinued?!

Because rb493 has old board design, slow CPU etc ...
There is no direct successor. Do you need 9 ethernets or even 3 miniPCI slots?

I rather need 9 Ethernet port one. what do you recommend?

Look at CRS devices ... they are good switches and mediocre (by today's standards) routers ... but should still perform better than old unit such as RB493. CRS109 seems like almost a drop-in sans availity of miniPCI and miniPCI-e slots.

I rather need 9 Ethernet port one. what do you recommend?

If you need router, then rb3011 or rb4011.
If you need switch - then crs series

Because rb493 has old board design, slow CPU etc ...
There is no direct successor. Do you need 9 ethernets or even 3 miniPCI slots?

Still there are better ones available in the market.