As an AI language model, I do not have personal experience or opinions, but here are the top 10 real estate platforms or apps for exploring investment opportunities in commercial office spaces based on research:

1. LoopNet – Commercial real estate marketplace with a wide range of investment opportunities across the US.
2. CoStar – Provides industry-leading commercial real estate information, analytics and marketing services.
3. CBRE – Global real estate services provider with a focus on commercial office spaces.
4. Realtor.com Commercial – Commercial real estate listings with a focus on office spaces.
5. Ten-X Commercial – Online marketplace offering a range of commercial real estate properties, including office spaces.
6. CREXi – Commercial real estate marketplace with a range of investment opportunities for office spaces.
7. Zillow Commercial – Online marketplace for commercial real estate listings, including office spaces.
8. Brevitas – Commercial real estate platform offering investment opportunities in office spaces and other property types.
9. Showcase – Commercial real estate marketplace with listings for office spaces throughout North America.
10. RealNex – Commercial real estate software and marketplace with a focus on office spaces.