Tahoe Diamond BLOG include stories about the areas.

Sledding areas: 
These areas are undeveloped - sledding is at your own risk. It is Free, but bring your own equipment.
Mt. Rose: Mt. Rose Highway (Hwy. 431). Undeveloped area 8 miles up.
Spooner Summit: Hwy 28, just off of Hwy 50 (about 9 miles south of Incline Village). Steep.
Ski and snowboard rentals:
Save by renting your ski equipment at VILLAGE SKI LOFT for as low as $24/day (compare with $39/ day at the resort). This rental place is within walking distance to this vacation home in incline village. Junior packages are offered as low as $14/ day and there are other incentives. Contact the place directly for more information.
Diamond Peak Shuttles:
There is a shuttle to dimond peak according to the following web site: http://www.diamondpeak.com/mountain/ski_shuttle. The closest stops on the list are All Seasons Condos and Raley's center. I have never used it in person and prefer to drive 5 mins to Diamond peak. If you prefer not to drive, consider driving to Hyatt which is very close and then take the shuttles from there. Those shuttles leave every 30 mins, which is much more reliable. Go to http://www.lake-tahoe-vacation.com/ski-resorts to get a better idea from the map. Please contact the Diamond peak directly to confirm or collect more information.
Summer beach access:
There are two private beaches for incline village residents and renting this vacation home entitles you to access as guests. You can visit Incline Village beaches for directions, access fee, and other information. You need to contact us in advance to mail signed guest access to you. For longer stays, we offer punch cards with 50% discount on beach access. That is more than $160 value for half price (while supplies last).
Summer activities:
Biking is a popular activity and VILLAGE SKI LOFT is the closest bike rental to this condo. If you are with kids and need a wider variety of trailers or tandem bikes, try OLYMPIC bike shop  in Tahoe city (25 mins drive). They also have easier paved tracks close to Tahoe city more fitted to family needs.
Hiking, water rafting, parasailing, water ski (instructions or practice), and jet ski are other potential activities around Tahoe for summer. A simple google search gives you the best spots arount north Tahoe for those activities.