While there are a lot of free messaging apps out there, if you have a lot of different groups of friends or loved ones (family, college classmates, workplace friends, party friends), then those that specialize in group messages is the one you're looking for. Microsoft's GroupMe is one of the more popular ones out there and the latest update brings a new design (take a wild guess what it is) and an important feature for those who keep "forgetting" important events that you've talked about.
If you're maintaining a lot of different groups and conversations, chances are you might forget some important appointment or event that you've talked about in one of your chats. Or you're getting annoyed with people who keep forgetting. Now GroupMe has a calendar feature that will remind users of things they've agreed to go to or participate in. Simply add an event, put a description, add people, input the location, even add photos like invitations or outfit pegs or gift suggestions. And it will also be posting reminders to participants so no one has an excuse anymore if they missed an event (unless they really intended to miss it).
In terms of design, GroupMe has succumbed to the inevitable. The app is now sporting a spanking new Material Design, following the guidelines that Google has been strongly suggesting to apps for Android devices. If you're one of the lucky ones who are already on Android 5.0 Lollipop, then the update would match up pretty nicely with your device's "new look" and new features as well.
If you're not yet a fan of GroupMe, you can download it for free from the Google Play Store. If you already have it, the update should be rolling out to you anytime now.