Formal & Legal:
* Complaints
* Charges
* Injustices
* Wrongs
* Claims
* Disputes
* Appeals
Informal & Personal:
* Complaints
* Grudges
* Discontent
* Dissatisfaction
* Resentments
* Misgivings
* Heartburn
More specific:
* For workplace situations: Dissatisfactions, Concerns, Issues
* For personal relationships: Disagreements, Quarrels, Rifts
* For political or social issues: Injustices, Oppressions, Abuses
The best synonym to use will depend on the context of your writing or conversation.