In /etc/services
on a few machines I've checked, port 9898 is associated with a service called MonkeyCom:
monkeycom 9898/udp # MonkeyCom
monkeycom 9898/tcp # MonkeyCom
The first reference I found in a google search for MonkeyCom says it's part of the Sasser virus. That seems like a misinterpretation to me -- it's more likely that Sasser is using 9898 but that there's some older service called MonkeyCom which originally got the assignment.
Who can tell me what MonkeyCom is?
Tripwire Enterprise uses 9898 as it's default port for communication between server and agent.
MonkeyCom is (or was - as far as I can determine it is now defunct) a videophone/file transfer program.
As far as I can determine nothing legitimate is currently using port 9898 - it's pretty much just Sasser and a few other bits of nasty.
pgpool might be using that port.
You can do a "lsof | grep 9898" and check.
The definitive source for Port Assignments is IANA http://www.iana.org/assignments/port-numbers from which you can find a name and email address of someone who might know the answer to your question. More probably the email address is no longer valid :-(
Echoing RedGrittyBrick's point. Came across the same. MonkeyCom is a port association for a legitimate program which is likely also exploited in other instances.
Check out the following listing for a bit more detail