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petetx - the
Reading List plugin is very useful for maintaining arbitrary lists.
I often create them by doing an external content search (I mainly use X1 or Windows Search), then the
Drop Search Results plugin to Mark the 'found' books, and then add the Marked books to a Reading List.
Added: If you just want to 'gather' a few books into a 'pile' temporarily, you could use the Mark Books feature. The Marks are NOT maintained between calibre sessions.
BR