Gmail tools
Indie products their makers tagged "gmail", most upvoted first.
IndieNeed is a launch site for indie makers.
The most upvoted products on IndieNeed with this tag. Tags are chosen by each maker.
Ranked products

Gmail Filters
Describe the filter you want in plain English ("label receipts from Amazon and skip the inbox") and Gmail Filters writes the native Gmail filter rule, so you don't need to learn Gmail's search syntax.
Browse the best tools by category or every product.