The SteemFriends app http://steemfriends.org started 2 years ago. Here is a list of things it can do:
Rank your top contributors in dollars between 2 dates:
Display side by side, between two dates, who votes for you and who you vote for the most:
Search through a list of articles you have written or upvoted between two dates, using tags or titles
Display the conversation record between you and a friend
Display your ranking for Followers, Reputation, Effective SP, Own SP, SBD, Estimated Account Value, Pending Payout, Past Payout, Power Down, Account Creation, Witness Voting Power on Steemit
Display how much you have contributed to a friend in $ between 2 dates and vice versa, broken down by articles.
To continue this service, the backend database steemsql costs 20 SBD per month. In the last few months, the SBD revenue from articles posted under this account plus the SBD payment from https://steemit.com/@thesteemengine has been keeping it going.
If the SBD amount of this account goes over 20 SBD, 20SBD will be transferred to steemsql to pay for the backend database for Steemfriends. Otherwise, thank you all for your support in the last few years! And lastly thank you to @thesteemengine and @enchantedspirit for keeping it going via the SBD payments. It's been fun making this. @magicmonk