The hosted version of WordPress at WordPress.com does not give you the option to install whichever plugins you want. Instead the service comes with a preselected set of options. A number of these options appear somewhat different to the individual plugins that are available for the self hosted version of WordPress.
In fact you can get all of these additional features that the hosted version of WordPress offers to install into your own copy but you do need a WordPress.com account to be able to enable them. WordPress provide all of the additional features from their hosted version as a plugin called JetPack. The only restriction on being able to implement these features on all of your WordPress blogs is that you need a WordPress.com account to be able to activate them.
So what sorts of things that are built into the hosted version does JetPack make available for all your WordPress blogs?
While JetPack implements all of the features in one package, you actuall get a choice with most of them as to whether you enable the feature or not and for those where they are enabled automatically you get to choose how they are configured.
Perhaps the most obvious of the various features that JetPack offers (and the one that first caught my attention) is the "publicize" option that is configured via the "Sharing" page in your settings. THis option allows you to have all of the posts you make on your blog automatically copied to any or all of Favebook, Twitter, LinkedIn, Tumbler, Path, and Google+. While there are alternative plugins that will allow you to individual social media sites that in some cases offer greater flexibility in what gets posted, this is the only plugin that offers all of these in one plugin.
There are a huge number of other features that JetPack provides so it will probably take you quite a while to go through all of them to dicide which ones you want to implement on your blog. You may also discover that there are JetPack features that duplicate or partly duplicate the functioning of other plugins you already have installed.You will then need to decide whether to keep using the previously installed plugin or whether to turn on that feature in JetPack and to uninstall the other plugin. Just which way you decide will depend on just how closely the features correspond to what you require. For example the Twitter feed I was already using allows me to have some categories of posts sent to Twitter while omitting other categories so I don't have to individually select which posts get transferred but can have the choice made automatically based on the category. The JetPack send to Twitter option doesn't appear to have this feature and so I will be keeping the old plugin for that. Another I need to choose between is the Avatar option in JetPack and the plugin I am currently using for accessing Avatars. Where the two are very similar there are pros and cons to both approaches as using the JetPack version will reduce the number of plugins you need while sending information via WordPesss.com while using a separate plugin means that you have more plugins but are less dependent on WordPress.com.
Installing JetPack on your self hosted WordPress blog provides you with a lot of options not otherwise available as well as alternatives to some that have been made available through third party plugins. While JetPack can't replace all of your other plugins it will increase what you can do with your blog and possibly do away with the need for some of your other plugins.