Offer me an open-source time-tracking software

This is a research work in which you are required to go through open-source software on the market, analyze it and offer a version which fit the requirements below. No development work is required. There are many time-traking software variants are there on the market. I need software with following features: 1. Support multiple users. 2. Have web ui. 3. Captures desktop screenshots. Screenshots should be taken at specified time intervals configured via web ui. 4. Easy to use. 5. Open-source. You should present at least 3 software solutions.