Toggl offers a Chrome browser extension with support for multiple services such as Asana, Gmail, Github, Slack and Wordpress. A full list of compatible services can be seen on the Github page.
The UI hides unnecessary clutter until you need it, but it is not hard to find later. For example, to start a new tracker, rather than having a separate list of favorite/recent tasks you can click on to continue, it has a "play button" triangle pop-up as you hover over each item in your day's agenda. This effectively doubles the screen space in the agenda over competing apps. Another example: the start-end date picker for choosing a reporting interval. Rather than having two fields you must click on and make sure you put the start date before the end date. It just has one calendar pop up. Then you click the start date first and the end date second. (One quibble: Monday is always the first day of the week, which can be jarring if the rest of your software uses Sunday). There are shortcuts at the bottom for frequently used ranges: "this month", "last month", "today," "yesterday", etc. And all of this hides itself in a simple text box until you click on it to edit the time. The interface for modifying times of previous entries is also wonderful. It guesses the right day when I enter a new time 99% of the time. After using Toggl's UI, you will be spoiled for every other tracking app.
The "starter" paid version (needed for sub-projects, billing, etc.) costs $9/month/user as of Feb 2018. This is several times the price of primaERP, which another user marked as too expensive.
The integration with Zapier allows for timers to start or stop based on triggers from many different apps.
For a list of possible zapier workflows, see https://zapier.com/apps/toggl/integrations
Toggl offers an API to allow for customization and extension.
For example, this allows for an iOS Workflow, that lets the user start and stop timers from anywhere, Workflow is available (Apple Watch Complication, Home Screen Icon, Launch Center Pro, Widget...)
This also means, that automatic start and stop of Timers are possible.
With easy integration into things like Google Calendar or Trello users will not have to spend much time setting up this time manager into their workflow.
The entire site needs a serious UI/UX upgrade. Almost every page is cluttered and unfocused - as if designed by an engineer (of which I am one, so I know how I naturally design things). They need someone to split the pages into more focused units that are quicker to scan and use.
The reports are cluttered and hard to scan and turn into usable information. They do have a banner of what the designers thought you'd want to see. But that banner is useless to me and the most important information for me (time use by task and project) is buried in small print and broken by total columns and there is no option to surface it.
Everything in TMetric is simplified for user convenience. You can easily track how much money you earned working with your clients. This feature gives you a perfect overview what clients give you the most income.