There appears to be a fork here:
https://github.com/rastaman/jira-mylyn-connector
Context
This is a fork of the probably discontinued Atlassian IDE
Connector for Eclipse which work on Eclipse 4.8. It has been tested
with MacOS and Linux and as Java code it should work everywhere.
Target JIRA platforms
The connector has been lightly tested with JIRA
6.3.1 on-premise and Atlassian Cloud.
With a single release in 2018 labelled:
eclipse-connector-3.2.5.201808261123.zip
I've not tried it yet as my setup using the details on this answer to get the last release from Atlassian, and Eclipse 2020-03 (4.15.0), was working with JIRA on premises.
However we've recently migrated to JIRA Cloud and although it connects I now get this error trying to synchronise task lists:
org.codehaus.jettison.json.jsonexception jsonobject["name"] not found
I assume this is some mismatch between fields in the connector and Jira Cloud so I'll report back here once I've had time to try the forked connector.