Nice post that you shared! I think with the trend of more urbanization, upper-middle class millennials have substituted some of the aspects of country clubs (social community mixed with athletics/sports) with expensive boutique group sports and fitness experiences like CrossFit, SoulCycle, and perhaps Equinox. Some of the true upper class friends I have still do things like pay dues for expensive social athletic clubs.
FWIW, right now I just use a combination of Evernote and a Trello board to keep track of personal tasks and projects; I could see a "PRM" tool like this supplanting or complementing those other tools.
I hope you keep building. Feel free to reach out if you want some user feedback in a few weeks.