I think Personal Knowbase might do just what you are looking for. On the left you have a column of "keywords" while on the right you have the plain article. Each article can have any number of keywords, you can just add any newly relevant keywords when you add the article.
With a number of articles added you can "drill down" and find any that has any combination of keywords, such as August, @errands and Dog, for example.
I find it useful and their website is www.bitsmithsoft.com if you fancy taking a look to see if it would help.