I also make use of the Metamask wallet. I don't know if they are open source, but it's been part of the oldest wallet I have been making use of in the past, and there is no problem. It has both desktop and mobile compatibility, but the desktop version has more features built into it than the mobile version.
Metamask is also open source wallet but it doesn't come in the form of an application but in an extension form that supports limited networks compared to other service wallets but its still one of the best for token storage but only due to the limited network and not having dedicated app even after all these year is a negative in my opinion.