I’ve been using Clockify as a standalone time tracker. It’s got Asana integration (a timer button appears in Asana via Chrome extension) so tracking time is quite convenient.
I simply start a timer, and when I’m finished, I go to the app itself to associate each time entry with a project (they don’t necessarily correlate with projects in Asana).
But the best thing about Clockify is that - unlike all the other apps (like Toggl, Harvest, Timecamp) - Clockify is absolutely free and lets you have unlimited users.