We use skype at work. Well, we used to now we use Lync. But, I still use skype. It is free. I think that there are some situations where there is a charge, but I haven't run into that yet. I use it for messaging and video chat where two computers have a 'call' so that my parents can see my daughter while talking to her. DD likes showing them her toys.
I really like it. One hint. Don't put ANY information at all in your profile and make up a fake name. Just putting your gender in there will allow people who are catfishing to find you in a search.
My husband and I use it instead of texting. Sometimes I'll be at work and think, "Oh, I need to tell DH (blah-blah-blah)" and I'll send him a message, then he'll it next time he's on the computer.
When you send a contact request to someone, you can send a message saying who you really are.