The $\eta$ and $\eta$' mesons are almost unique in the particle universe since they are Goldstone boson and the dynamics of their decay are strongly constrained. The integrated eta meson samples collected in earlier experiments have been about $\sim10^{9}$ events, dominated by the WASA at Cosy experiment, limiting considerably the search for such rare decays. A new experiment, REDTOP, is being proposed, with the intent of collecting more than 10$^{13}$ $\eta$/yr (10$^{11}$ $\eta'$/year) for studying of rare decays of these mesons. Such statistics are sufficient for investigating several symmetry violations, and for searches of new particles beyond the Standard Model.