With so many other recommendations in this thread I thought I'd say that I've used FreeOTP for several years now. Currently I have 10 "keys" in it that I use daily.
Never an issue and I enjoy using an open source product backed by my favorite company, RedHat.
I've used it for years with 25+ keys, and it gets a bit unwieldy. The main problem is that the only sorting mechanism is manual, so I can't sort by last used, or search the keys by name, so I keep having to read the entire list every time to find the key I want.
Never an issue and I enjoy using an open source product backed by my favorite company, RedHat.