Only the current version so far — new entries appear as the app ships updates.
Astable 555 Timer is a productivity app by Randle Christian Sink with 1,000+ downloads (about 3.5K estimated). Released Nov 19, 2014. Install growth, rank history, SDKs and ad networks.
From the store listing: “Enter Ra, Rb & C to calculate hi & lo duration, frequency and other values...”