Redmine

Some of our biggest "problems" that causes us to look elsewhere for a solution are:

• there is no way to use an "OR" clause.
• there is no good way to search for multiple issues (its possible to select multiple trackers, statuses, etc. but it is not possible to select multiple subjects nor is it possible to define separate filters per selected filter (e.g. different assignee for each selected tracker) and other similar use cases).

One proposed solution:
I think one of the "more simple" methods of adding this feature would be to add a way to define multiple sets of "queries"/filters in one search:

Ex. you need to search for two types of issues at once. Tracker A that are assigned to Paul and Tracker B that are assigned to John. You need to see both of these side-by-side to be able to compare the due dates between the two and take action as needed.
You define your first "query"/filter by filtering for Tracker: "A" and Assigned to: "Paul". After that, you click a "+" icon below the filter/options that adds another set of filter/options and you can define your second "query"/filter by setting Tracker: "B" and Assigned to: "John". Click apply and it will run both queries, distinct & union the result set and display accordingly. The displayed columns would be shared between all issues.

This could also lead into some sort of combined custom query searching capability if that is something you guys want to explore.