One good option is SoWork, which has a range of tools to improve communication, productivity and participation. It includes high-end videoconferencing, AI-powered meeting tools, customizable offices and integration with tools like Google Calendar and Slack. SoWork offers a free version for up to 10 people and paid options starting at $6 per person per month, so it should be good for small, medium and larger teams.
Ploito is another interesting option that tries to re-create the feel of an actual office with live avatars that indicate who's in and virtual rooms that you can assign to employees. It's also got tools for assigning tasks, sharing screens and keeping an eye on burnout. Ploito costs $8 per active employee, but it's free for companies with up to 4 employees, so it's a good option for small to medium-size teams.
If you want something more social and community oriented, Litespace has tools to engage employees, build community and schedule meetings. It's got engagement tools, automated scheduling and centralized analytics. Litespace is good for teams that want to try to keep employees engaged and try to get a handle on their remote work schedules.