I just built Ponder (https://ponder.chat): it's like Slack, but you're the only one in the chat! I wanted to be able to work through ideas and problems in a timestamped chat interface, as well as to dump in random thoughts/links/todos/etc. without worrying about what document to put them in. Any message can be retrieved with search and hashtags.
I'd love to get your feedback on Ponder! If anyone could register and use it for a day, I'd be particularly grateful!