BucketList.net - Bucket list ideas, advice and support
Freeplane - Freeplane is a powerful and free software for building mind maps.
Life Listr - ***AS FEATURED BY APPLE***
Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.
Bucketlist.org - Log and catalog all the stuff you want to accomplish before you expire.
OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.