Kepler Custom Fields is a suite of free custom fields that we found very useful when working with JIRA.
The plugin offers a suite of custom fields that we think should be part of every JIRA installation. These will improve the user experience and will allow you to customize JIRA to better suit your needs.
Included custom fields:
The Interval Custom Field offers a JIRA-styled time interval custom field. It allows you to store time interval values in a way that is consistent throughout JIRA.
Provides a calculated custom field that uses the power of SIL scripting. It allows you to configure a SIL script for each context to calculate the value of the custom field.
Offers a text custom field that is validated using a configurable regular expression.
Shows the logs for the current action on the issue.