There are several platforms and tools available for closed captioning, which is the process of adding text captions to audio and video content to make it accessible to individuals who are deaf or hard of hearing. Here are some popular platforms and tools for closed captioning:

1. YouTube: YouTube offers automatic captioning for videos uploaded to the platform. While automatic captions are not always perfectly accurate, they can be edited manually for better accuracy.

2. Amara: Amara is a popular online platform for creating and editing captions for videos. It supports collaboration, making it useful for teams working on captioning projects.

3. Rev: Rev is a professional transcription and captioning service that offers accurate and fast captioning services for various types of content, including videos, webinars, and more.

4. 3Play Media: 3Play Media provides a suite of captioning and transcription services, including automated and human-generated captions, along with tools for editing and managing captions.

5. CaptionHub: CaptionHub is a collaborative platform for creating and managing captions and subtitles. It's designed to streamline the captioning workflow for teams.

6. Kapwing: Kapwing is an online video editing platform that includes tools for adding captions to videos. It's user-friendly and doesn't require advanced technical skills.

7. Adobe Premiere Pro: If you're looking for a professional video editing software, Adobe Premiere Pro includes features for captioning and subtitling your videos.

8. Aegisub: Aegisub is a free, open-source software specifically designed for creating and editing subtitles and captions for videos.

9. SubRip (SubRip Text): SubRip is a widely used subtitle file format and a tool for extracting subtitles from video files. It's a basic but effective option for captioning.

10. Facebook: Similar to YouTube, Facebook also provides automatic captioning for videos uploaded to the platform. As with other automated systems, manual review and editing might be necessary for accuracy.

Remember that the level of accuracy and ease of use can vary between platforms and tools. For critical projects or content with high accessibility requirements, it's often recommended to use professional captioning services or platforms that offer a combination of automation and human review for the best results.