The PlayCanvas engine is free and open source. However some of the tools (such as private projects and native mobile support) are subscription based. Prices range from $15-$60/month for personal, and $100-$400/month for organizations.
Famous is young, and currently not one of the more popular options. Due to the chance of undocumented bugs and the lack of community support, some developers still feel it's a bit too early to use. However, Famous is under active development and the community is growing.