Hacktoberfest 2021 is a month-long celebration of open source software hosted by DigitalOcean, where developers can contribute to various projects, including Symbl.ai, and earn rewards such as developer swag and exclusive stickers. During the event, Symbl.ai will be accepting development contributions on three repositories and providing feedback channels for users to share their experiences. Contributors who raise multiple issues or PRs may be eligible for a t-shirt, while those who fill out a contributor submission form will receive swag. The event aims to support open source software and quality contributions, and Symbl.ai maintainers are available to answer questions on Slack or GitHub.