This is a loaded question! Depending on what you do of course the answer will vary.
Im the founder and CEO of a Robinhood marketing agency, dubbed www.Unthink.me - We bring big business marketing tools and strategies with small, growing companies. My schedule is very different than that of a CEO in my position.

For example, I am very hands on the projects we have, just the way I started my business, as it grew my name got very attached to the brand and thus a lot of our clients hire because they want me to help on a campaign or project, so I wake up around 4am, check my email and my SLACK - which is how me and my team communicates and keeps our conversations seperated from client's convos and per project.
I respond to emails and check our Hubspot platform, hangout with my kids then around 9am head to the office where I have a 1 hour coffee & convo with entreprenurs all over the world through a seperate #SLACK channel.

Then I check TRELLO - for project management work and follow up on issues I see through Slack as well.

I use my Text Messenger App a lot actually to send myself notes through text - i don't open them up until I am ready to take care of them, since I text other people, this is a clever way for me to easily get reminded of a task w/o getting annoyed with the reminders (this would be an awesome app btw! If you're looking for ideas, lets get this one going!)

Aside from those that dictate how I work, I use Dashlane a lot to save me time entering passwords, etc - especially for other clients.
That's about it, maybe Google Calendars, but don't use it unless is for something way ahead in time.