I have designed a communications and documentation management platform in the past which used inline filtering within the search bar and a drop down assistant that guided the users through the various filter options. Similar in a sense to the slack search if you have used it before.

Using text prompts such as 'in', 'after', 'before', 'has' followed by a qualifier key such as ':' or '+' then the users filter criteria. Very time efficient for power users.

Obviously depends on the range of items you wish to filter by and how they are structured. But the client was looking for something innovative as well, seemed to make them happy...