Optimism produces its own wallet software package that is readily available for down load on its website, which allows you to store Optimism on your own computer. For maximum stability, you could store your cryptocurrencies over a committed hardware wallet like a TREZOR wallet or simply a Ledger Nano https://financefeeds.com/what-makes-blockdag-better-than-traditional-blockchains-advisor-mit-alum-dr-maurice-herlihy-reveals-all-in-new-ama/