It does not matter whether you are building an outdoor or an indoor playground; the main features still remain the same so does the playground equipment. Of course there are the slides, but that is another subject and you can find a bit longer piece on it also on this page.
The playground equipment may differ concerning the age of the children using the playground as some things that are completely safe for older can be a terrible hazard for smaller. Therefore, always take into account that point when choosing playground equipment.
But now about the playground equipment you should have. First of all definitely somewhere to climb, for example a net or some kind of a climbing tree. This develops your child's coordination and makes him or her move more than just using a slide. Secondly, you should without doubt have a swing or even more, because you can probably remember from your own childhood how much fun was it to swing for hours.
In addition, if you are building an outdoor playground, it is not very hard to add a sand box, but your child will certainly be thankful for that.
These have been only the main playground equipment that should unquestionably be in a playground, but use your imagination and think what to add to make the playground more unique and more fun for your child.