BOINC was designed and is still mainly used for scientific projects. 
Golem is designed to support all types of project that people may want to pay for.

Gridcoin is a cryptocurrency itself, Golem is not. It’s more a computational power market, where you can define your own prices and payments are made using external cryptocurrency ETH. Remuneration in gridcoin come from mining GRC not from project creators and because GRC itself is not widely adapted doesn’t have much value.