TubePen

TubePen allows users to highlight and annotate YouTube videos, which can be considered a form of timestamped comments or notes on video content. However, it does not offer screen recording, camera recording, or instant shared links of original content, which are core 'must-have' features for the described concept of an asynchronous video communication platform like Loom. Its primary function is to enhance learning from existing YouTube videos, not to create new video messages.