Reference management tool with ability to add custom fields I am currently trying to manage around 100 references from ISI Web of Knowledge. To manage them in a useful way, I need to manage a table, one row for each reference, with 4-5 user defined structured columns (like: which climate variable they correlated with which demographic variable etc.). 

So for this purpose I need to add custom fields to each reference; then display the table of selected references, and be able to sort and filter using these fields. Is there any reference manager that supports this? Unfortunately Zotero doesn't and is not going to.

PS: Of course I don't like the idea of having separate excel table besides. I would then miss the comfortable link between the table rows and the PDF and personal notes and other things which I manage through the reference manager (currently Zotero).
I'm not sure if this would be enough for you, but in Mendeley you can add multiple tags to every reference and then you can filter them using those tags (just type it in a search bar).
You can also add a note to every reference, and use those to filter your references.

In both cases, it should be something unique, so you don't get unwanted search results.