I use Tweepi because it has “date followed / unfollowed” and you can give people time to follow back before deciding to reintroduce yourself or unfollow them. (if follow backs are a part of your strategy). The downfall is it is $15.99/ month. 

Do you know of any other apps that tell you which date you followed someone?

Yeah  @rich-brooks , for selfish reasons, I was real bummed to see One Forty go down. I was really active there. It is a huge leap from all the free “stuff” on One Forty to the corporate price tag of Hubspot. I have not had a chance to test drive Hubspot. (this will be my next forum topic) 
Back to the initial question, if anyone finds any another Twitter apps that monitors “date followed”, please post it on this thread. 

FYI, you can still access the OneForty data, which is amazingly comprehensive, though depreciating rapidly.  You can get it here if interested https://github.com/HubSpot/oneforty-data