Most apps designed to bring people together are also designed, more quietly, to keep you on the app. Perihelion is for the simpler thing: making it easier to ask your friends to do something together.
Inviting is asymmetric work. The friend who plans things notices nobody has seen each other in a while, picks the place, sends the text, and fields the half-replies. Group chats reward the loud; event platforms turn casual hangs into productions; calendar invites are for meetings.
Perihelion makes one structural choice and lets it ripple: friends opt in once, on their own terms. Every later invitation is something they already agreed to receive. The organizer is freed from feeling like a burden, and the invited friend can decline simply by saying nothing.
There is no feed to scroll, no streak to maintain, and no discovery engine. Notifications arrive by email, immediately or in a daily digest. SMS is planned, but it will stay off until the service is approved to send it responsibly. When the plan has been made, the right thing to do is close the tab.
It works for old friends and for newer friendships that need a little room to grow. Inviting somebody you barely know to do something casual is one of the highest-friction asks in adult life. Reducing that friction is a good in itself.
Perihelion is a small, open-source, non-commercial utility built by Sarah Lewis. It does not run ads or sell your data. If it helps you see your friends more often, that is enough.