I don't wish to appear pedantic, but this topic should read "Symbian Tools and SDKs".
Apostrophe s means possessive or abbreviation, for example:
"this tool's documentation" (the tool possesses documentation)
"these tools' documentation" (the tools possess documentation)
"this tool's undocumented" (this tool is undocumented)
To pluralise a noun, you don't add an apostrophe. Pluralisation of acronyms and abbreviations such as "SDK" aren't even necessary, but most people use them to avoid confusion.